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Archive for the ‘Electrical power’ Category

What’s inside a smart meter?

Wednesday, February 22nd, 2012

You can usually find the folks at iFixit tearing down electronics with an eye toward expanding your knowledge of how to repair your electronic devices and keep them out of landfills by extending electronics’ life span.

What’s inside a smart meter? iFixit tears it down article tells that the technicians at iFixit got their hands on an Elster Rex2 Watt-hour meter and they had opportunity to evaluate the health and safety issues that seem to surround the utilities’ installation of smart meters. This smart meter has nonvolatile memory, advanced security with encryption, the ability to make remote upgrades, and support for 900-MHz and 2.4-GHz ZigBee communication.

The Smart Grid depends on smart meters with sophisticated communication capabilities to monitor energy usage and allow residential and business consumers alike to make informed choices about how much energy to use and when to consume it.

Posted in Electrical power, Electronics Design | No Comments »

Fused multimeter probes

Thursday, December 29th, 2011

This is my second product test on Free Product Road Testing program by Farnell. This time the tested product is fused test leads for multimeter (Farnell Number: 428-4276).

42265381

Why Fused Leads?

You might ask why test leads need be fused. Trust me there are situations where this is a really good idea. Maintenance of electrical and electronic equipment exposes the technician to potentially lethal voltages and short circuit current. Multimeter have fuses inside them, but those fuses do not always provide enough protection. Stock Multimeter Explosion video illustrates what happens when the fuse inside multimeter is not enough protection. This failure takes place in milliseconds and leaves very little time to react to the mistake as you can see in the picture below (image capture from Stock Multimeter Explosion video).

multimeterfail

If you plug the leads in the wrong spot or have the wrong settings this is what can happen. It all depends on the interrupting capacity of the fuse on the meter. Very many multimeters have cheap fuses that can’t interrupt high current fault. Most commonly used 5×20mm glass fuses often seen in cheap multimeters have a low breaking capacity which generally restricts them to applications of 15 A or less at 250 VAC (Bussman fuse specifications say interrupting rating 35A at 250V for 32mA – 3.15A fuses). Ceramic fuses have the advantage of a higher breaking capacity due sand fill inside fuse body, but they cost considerably more than basic fuses. Not all fuses of the same amperage and voltage rating are the same! Unless a meter was specifically designed to meet CAT III-600 V or higher, it is not safe to use on power circuits.

Fused probes provide an additional level of measurement protection when making voltage or current measurements. It is safest is to use fused probes that have fuses with high enough interrupting capacity. Excessive current drawn through test probes, leads and measuring instruments can happens when a multimeter is set to the wrong function, eg. set on a current or resistance range when you should measuring voltage. circuit. But luck is not much to count on, especially when you could avoid the problem altogether by using the proper fuse.

The short circuit currents on electrical systems can he huge. If you take a CAT III 1000 V meter with the test leads in the amps jacks, you will have a series resistance of approximately 0.1 ohms between the leads. If you accidentally place the leads across an ideal 1000 volt source, you will generate a current of 10,000 amps. In real life electrical systems the electrical distribution network impedance will limit the current to somewhat lower but still huge (short circuit current easily 20-100 times higher than normal current on the circuit). This huge current can cause serious damage including multimeter explosion and test leads start to melt in very short time. When you can’t count on the multimeter to have the proper fuse, the best idea it to get fused probes that for sure have proper fuses in them. When you make that simple mistake of putting voltage across the current jacks and blow the fuse, you’re at first thankful you didn’t wipe out the meter or get hurt.

ESA commissioned a series of tests to simulate the impact of using fused leads as a protective measure. Fused leads used with multimeters prevented possible catastrophic results when the meter was used in an inappropriate way or experienced an internal failure. Fused leads worked as a safety mechanism in 90% of simulated tests. Eventually everyone tries to measure volts with the amperage setting. With a good fused multimeter probes (and other necessary safety accessories) you won’t do any serious damage. Adding to the user error problem is wear, tear and contamination within the meter that creates internal component failures or compromises the components’ dielectric properties. Multimeter Accident Prevention Plan, An Electrical Inspector’s Survival Guide article tells how people working with electricity are getting hurt using multimeters and how to eliminate or limit the risk.

British HSE guidance GS 38 (mentioned on fused probe documentation) and Canadian Electrical Safety Authority (ESA) drive to adopt fused test leads as an added safety measure for those doing electrical testing with multimeters. It is necessary to use leads which incorporate high breaking capacity (hbc) fuses that nadequately rated to deal with short circuit energy present on electrical power systems. Also batteries can cause a high energy flashover when short circuited, so fused leads are also good idea when working with large battery systems.

In addition to fusing you need to consider other design design features of the probes. The standard multimeter leads typically have an excessive length (usually around 15-19 mm) of bare metal at the contact end. This kind if probes can accidentally too easily bridge a live conductor and adjacent earthed metalwork with disastrous consequences like arch flash on high energy circuits. So keep the normal multimeter probes away from such circuits.

Finnish electrical safety document STO 2/2009 says that for voltage measurements the voltage meter probes should have maximum 10 mm of exposed metal on the tip. GS 38 electrical safety booklet from HSE (UK) says that exposed metal tip on suitable should not exceeding 4 mm measured across any surface of the tip (recommended 2 mm or spring loaded retractable screened probes). EN/IEC61010-031 regulation (came into effect on March first 2011) says that test probe bare metal tip length is limited to a maximum of 4mm in measurement categories CAT III and CAT IV, and 19mm in measurement category CAT II (USA knows this as UL 61010-031).

Tested probe details

The SILVERTRONIC – 131247 – TEST LEAD SET product is a red and black fused lead assembly made up of double insulated silicone cable incorporating a fused probe assembly with a short fixed tip. The multimeter end is terminated with 4mm right angled fixed shrouded plug to reduce inadvertent hand or finger contact with any live test socket.

probe1

The product came in a simple plastic bag. A professional product does not need any fancy package.

probe3

The bag contained the test probes and one paper that tells the most important product technical details (some more details can be found from Technical Data Sheet).

probe2

SILVERTRONIC – 131247 – TEST LEAD SET is rated 1000V CAT III IEC61010. Each probe is fitted with a 500 mA/1000V/50kA fast acting ceramic fuse as standard. The probe documentation paper says that “lead set have built-in fuses for additional measurement protection” and the probes are fully compliant with GS38.

Fuse provides protection with a current limiting capability and and very high interrupting rating. The tested probes have suitable high breaking capacity (50kA) very fast acting (FF) fuses with low current rating (500 mA) housed in the probes themselves.

probe4

“Interrupt rating” (“breaking capacity”) refers to the maximum amount of instantaneous current that can be interrupted safely without explosion or damage. This interruption of current flow can occur in fault or short circuit conditions. Interrupting rating of fuses and breakers not be less than the maximum available short circuit current at their point-of-application.

probefuse

The 50kA interrupt rating is enough for very many electrical power applications. For example typical circuit breakers on home electrical panels have 5-6kA interrupt ratings and the short circuit currents considerable less than that. Typical fault currents in industrial applications can be well over 10,000 amps. The high interrupt capacity of the probes lies in hands of the supplied high breaking capacity 1kV 500mA 50kA fuses. If you happen to burn those fuses, use proper fuse replacements (do not try to put a “normal” 6.3×32 mm fuse there).

probetips

The bare tips on the supplied probes are short (around 2.5 mm) for a good reason. The 2.5 mm bare tip is well below that 4 mm GS 38 recommendation and shaped so that is pretty hard to make accidental short circuits with it. The probes being tested have good finger barriers guard against inadvertent hand contact with the live conductors under test. The probes feel good on the hand. Their handle are slightly thicker than in normal multimeter probes, which is not a bad thing at all. Otherwise they feel and measure pretty much the same as “normal” multimeter probes, they are just thicker.

The probe cables are insulated with silicon insulator and fulfill the double insulation requirements. The cable is very flexible which is very good thing (more flexible than cable on many “standard” multimeter probes).

One practical note that I found out then testing the probes is that the fuses inside the probes have some resistance in them. I found out that the multimeter resistance range showed 2.5 ohm loop resistance with the fused probes (versus zero ohms for original multimeter probes). If you plan to make resistance measurements with those probes, take this into account. The series resistance does not have any measurable effect on the voltage measurements.

The probes I tested seem to be good for what they are intended for. The price (29,68 €) seem to be reasonable because other similar probes seem to be cost at least the same or considerably mode (many other cost easily around 100 US dollars).

Posted in Electrical power, Products | 1 Comment »

AC current levels

Sunday, October 23rd, 2011

AC current levels

0.25mA  Maximum Leakage Current for Class II equipment in IEC 950 (Information Technology Equipment, I.T.E.) (no protective earth ground in the equipment, double insulation or reinforced insulation)

0.5mA Earth Leakage Current limit in IEC 601-1 (Medical Equipment) (this is general value, here are also other leakage current requirements in IEC 601-1)

0.5mA Perception level, tingling sensation,Perception level, tingling sensation

0.51mA UL limit used by UL for continuous 60-Hz sinusoidal current: Involuntary muscular reaction

0.75mA  Maximum Leakage Current for Class I (Hand held) equipment in IEC 950 (Information Technology Equipment, I.T.E.) (basic insulation and protective earth ground connect to case)

1mA A person can feel at least 1 mA (rms) of AC at 60 Hz

1mA Current of less than 1 mA (AC or DC) can cause fibrillation if the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode)

3.5mA  Maximum Leakage Current for Class I equipment in IEC 950 (Information Technology Equipment, I.T.E.) (basic insulation and protective earth ground connect to case)

5mA Typical GFCI limit in USA. Electric current below 5 mA is not considered dangerous.

5mA UL limit used by UL for continuous 60-Hz sinusoidal current: Involuntary muscular reaction

9mA The value of current considered dangerous was obtained experimentally, and is usually given as approximately 9 mA.

10mA Painful shock, freezing current, “can’t let go” (tetanized muscle)

10mA Residual current detector limit in use in Europe for sensitive RCDs.

20mA UL limit used by UL for continuous 60-Hz sinusoidal current: Ventricular fibrillation

30mA Typical residual current detector limit widely in use in Europe

35mA Heart rhythm affected (Ventricular fibrillation), death may occur

50mA Electric current above 50 mA is considered fatal in USA and Canada electrical safety regulations.

60mA  50 or 60 Hz AC current through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 mA.

100mA When 100mA is flowing through the body for only two seconds can cause death

200mA Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all.

1A Commonly used nominal output current for current transformers used for electrical power measurements in electrical power panels and distribution systems

2.5A Maximum allowed current for equipment that use “Europlug” (EN 50075) mains connector

5A Commonly used nominal output current for current transformers used for electrical power measurements in electrical power panels and distribution systems

6A Mains power fuse size (found on some old installations in Europe)

10A Commonly used mains outlet fuse size found in Europe (1.5 mm^2 wiring)

13A Maximum current available from electrical outlets in UK (maximum fuse size in fused plugs)

15A Commonly used mains outlet fuse size used in USA

16A Commonly used mains outlet fuse size found in Europe (2.5 mm^2 wiring)
16A Standard CEEFORM mains connector current rating (CEE 17 7 IEC 309)

20A Mains outlet fuse size used in USA for outlets (heavy loads)

25A Commonly used fuse size for incoming wire in mains distribution panels for small houses in Finland (three phase 400/230V power at 25A per phase)

32A Standard CEEFORM mains connector current rating (CEE 17 7 IEC 309)

63A Standard CEEFORM mains connector current rating (CEE 17 7 IEC 309)

125A Standard CEEFORM mains connector current rating (CEE 17 7 IEC 309)

Posted in Electrical power, Electronics Design | No Comments »

Common DC voltage levels

Thursday, September 29th, 2011

DC voltage levels:

0.7V Nominal voltage drop on normal silicon diode or similar semiconductor junction

0.8V Voltages from 0V to 0.8V are considered to be logic 0 on TTL logic IC inputs

1.25V NiCd, NiMH battery cell nominal voltage

1.5V Carbon and alkaeline battery cell nominal voltage

1.6V The voltage you normally get from a fresh alkaeline battery cell

1.8V Quite commonly used very low voltage digital circuit operating voltage (many CPU cores)

2V Lead acid battery nominal cell voltage

2V Voltages from 2V to 5V are considered to be logic 1 in TTL logic IC inputs.

3V Lithium battery nominal voltage

3.3V LVTTL logic circuits operating voltage

3.6V Typical voltage used to power cell phones (either from NiMH or Li-Ion battery pack)

4.5V operating voltage for many small electronics gargets powered from three batteries

5V TTL logic circuits operating voltage

6V operating voltage for many small electronics gargets powered from four batteries

9V Commonly used battery voltage

10V Normal control voltage limit in 0-10V and 1-10V analogue control systems (light dimming and industrial use)

12V Car battery nominal voltage

13.8V the voltage you expect to get from car 12V power when car motor is running (charging battery)

24V Truck battery.
24V Automation systems most common nominal voltage used for logic signals and and current loop powering

24V common standard input voltages in Avionics and Defense applications

28V Maximum battery charging voltage for 24V battery system (for example batteries that power automation systems).

28V common standard input voltages in Avionics and Defense applications

36V Battery voltage used on some electric golf carts, electric scooters, electric bikes, high power cordless tools etc..

42.4V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be SELV.

42.4V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)

48V Battery backed up -48V voltage is used on telecom systems for powering telephone exhanges and other telco equipment. The normal service voltage range for the -48 Vdc nominal supply at interface “A” shall be -40,5 Vdc to -57,0 Vdc according to ETSI EN 300 132-2

48V Some data centers use 48V DC to power servers (battery backup easy)

48V Phantom power feed for microphones in audio mixers most often uses +48V phantom power voltage
48V some automation systems use +48V power for equipment and I/O (electrical power distribution)

50V Work on energized circuits or apparatus below that voltage requires no “Hazard/Risk Evaluation.”     NFPA 7OE

60V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be SELV.

60V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)

72V standard input voltage in rail applications

75V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c

110V Seen on electrical power distribution control automation as IO voltage and for operating actuators on high voltage power distribution stations.

110V standard input voltage in rail applications

120V Extra-low voltage high limit is 120 V ripple-free d.c.

125V Commonly used insulation resistance testing voltage used for low voltage wiring testing where 250V test voltage is too much.

160V The highest DC voltage covered by the telephone/telecom/ITE industry is 160V (ANSI T1.311)

169V The peak voltage on 120V AC mains power is around 169V, you get around this voltage if you rectify and filter 120V mains power

220V Seen on electrical power distribution control automation as IO voltage and for operating actuators on high voltage power distribution stations.

250V Commonly used insulation resistance testing voltage. Tests on SELV and PELV circuits are carried out at 250 V.

270V common standard input voltages in Avionics and Defense applications

324V The peak voltage on 230V AC mains power is around 324V, you get around this voltage if you rectify and filter 230V mains power

380V DC power voltage for DC feed used on some data centers. Emerge Alliance pushes using this 380V system.

500V Commonly used insulation resistance testing voltage. Insulation tests at normal mains wiring (230V) is commonly tested with 500V test voltage. Minimum insulation resistance expected on mains circuit is 0.5 Mohm. Also test between SELV and PELV circuits and the live conductors of other circuits must be made at 500 V.

575V DC power voltage for DC feed used on some data centers

600V Voltage used on

750V Voltage used to power trains in Helsinki subway (third rail powering)    

1000V Commonly used insulation resistance testing voltage for circuits that operate above 500 V up to 1000 V.

1500V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c

2500V Commonly used insulation resistance testing voltage

3250V Use 2300V rms or 3250V dc test voltage for dielectric-withstand test for double insulation

5000V Commonly used insulation resistance testing voltage when testing high voltage wiring

Posted in Electrical power, Electronics Design | 2 Comments »

Commonly used AC voltage levels

Tuesday, September 13th, 2011

AC voltage levels:

0.316V The most common nominal level for consumer audio equipment is -10 dBV, 0.316 volts root mean square (VRMS).

0.7746V The reference voltage for the decibel unloaded (0 dBu) is the voltage required to produce 1 mW of power across a 600 ohms load (approximately 0.7746 VRMS)

1V  The reference voltage for the decibel volt (0 dBV) is 1 VRMS, which is the voltage required to produce 1 milliwatt of power across a 1 kilo-ohm load

1.228V The most common nominal level for professional equipment is 4 dBu. A signal at +4 dBu is equivalent to a sine wave signal with a peak amplitude of approximately 1.737 volts,or any general signal at approximately 1.228 VRMS.

12V A low voltage lighting system usually operates on 12 or 24 volts.

24V A low voltage lighting system usually operates on 12 or 24 volts.

24V Used for controlling relay coils in some automation and control systems.

50V Extra-low voltage high limit is 50V AC

warning-02

50V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500V DC

75V Typical telephone line ring voltage is 75 V a.c.(20 or 25 Hz), it could be between 40 and 150 Volts (15-68 Hz)

100V Mains voltage in Japan. Reference voltage level used on electrical power stations measurements (100V = nominal high voltage on line being measured)

110V Mains power in USA, the voltage you expect to get from mains outlet
115V Mains power in USA, the voltage you expect to get from mains outlet
120V Mains power in USA, the output voltage on the distribution transformer

200V If the voltage is less than 200 V, then the human skin is the main contributor to the impedance of the body in the case of a macroshock—the passing of current between two contact points on the skin.

208V The voltage you expect to get between two phases in USA in case our apartment
gets two phase wires from three phase transformer (208/120V)

220V Old European nominal voltage, harmonized to 230V

230V Electricity supplies within the European Union are now nominally 230 V ± 6% at 50 Hz

240V the voltage you expect get between two hots in USA on your hous
240V Old nominal mails voltage used in UK, harmonized to 230V
240V the voltage you get between two hots in USA on the distribution transformer

277V Voltage between phase and neutral on 277/480V three phase system, used in USA for example lighting loads on big buildings

400V Voltage between phases on 220/400V three phase system (old European system)

415V Voltage between phases on 230/415V three system (modern European system)

450V If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs

480V Voltage between phases in USA in commonly used 3 phase distribution

600V Three phase power voltage

690V Three phase power voltage used in industry for larger electrical motors (Europe)

warning-02

1000V Isolation test voltage for 130V rated working voltage basic isolation (IEC950)

1000V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c
1000V There phase power voltage used on 1 kV power distribution (in use in Finland)

1350V Basic insulation of 1350V rms is needed for test-and-measurement instruments rated at 250V (IEC 61010-1)

1500V Basic insulation of 1500V rms is needed for information-technology products rated at 250V (IEC 60950-1)

1500V Isolation test voltage for 230V rated working voltage (IEC950) (basic isolation)

2100V Isolation test rating for reinforced isolation for 130V rated devices

2300V Use 2300V rms or 3250V dc test voltage for dielectric-withstand test for double insulation

7.2kV Common distribution voltage in USA

10kV Common distribution voltage in Finland

11kV Common distribution voltage in UK, New Zealand and Australia

12.47kV Common distribution voltage in USA

20kV Common distribution voltage in Finland

25kV Electrical trains use 25kV 50Hz power in Finland

33kV Common distribution voltage in UK, New Zealand and Australia

34.5kV Common distribution voltage in USA

110kV Commonly used voltage level on long distance electrical transportation lines

220kV Commonly used voltage level on long distance electrical transportation lines

400kV Commonly used voltage level on long distance electrical transportation lines

Posted in Electrical power, Electronics Design | 1 Comment »

Power Quality Symptoms & Solutions

Monday, September 5th, 2011

Power Quality Symptoms & Solutions e-book is is written from an electronics point of view, rather than a power engineering one. And in so doing, provides the bridge between theory and real life. According to the book introduction more and more lecturers are using this material as a reference in their courses. You can find lots of interesting reading here for many industry fields and links to other resources.

2200a

booklogo

Posted in Audio and Video, Electrical power, Electronics Design, Groundloop | No Comments »

Smiling electrical outlet

Monday, August 15th, 2011

I visited Denmark in summer. This is normal grounded mains outlet I saw there. It looks just like a smiling face.

mains_danmark

Posted in Electrical power, Off topic fun | 3 Comments »

Weird Voltages in a PoE Camera System

Friday, August 12th, 2011

It seems that there is a trend to convert video systems over from an old, all-analog system to a modern, IP-based system with cameras powered over the Ethernet line using PoE (Power over Ethernet).

Weird AC Voltages in a PoE Camera System post at Control Geek Blog talks about an interesting PoE (Power over Ethernet) issue I found with some IP cameras and some switches.

Weird AC Voltages in a PoE Camera System–Followup gives some more details and analysis of the problem. And if you are really interested in the details check also Interesting PoE problem discussion at The Show Control Mailing List.

Posted in Audio and Video, Electrical power, Groundloop, Telecom and Networking | No Comments »

Power Quality and Utilisation Guide

Monday, June 7th, 2010

Power Quality and Utilisation Guide is a free on-line reference source for power quality information. It provides both background theory and solutions from electrical power industry. The guide is prepared by specialist authors from industry and academia, and edited by Copper Development Association’s David Chapman. The Guide is organized into 8 sections and presented in a series of short Application Notes. Application Notes are down-loadable individually in pdf format or as a fully searchable library (packed to Windows exe).

powersystem

Posted in Electrical power, Electronics Design, Groundloop | 4 Comments »

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