# Tag Info

98

It's a fault circuit indicator. Specifically, it's the Sentient MM3 model which monitors the current through the conductor it's attached to. It also draws its power from the magnetic field resulting from the current passing through the line. It logs and can wirelessly transmit the data it gathers which helps the local electric utility in quickly ...

54

The neutral is NOT safe to touch. When everything is working correctly, it should be at most a few volts from ground. However, and this is the big gotcha, if there is a break in the neutral line between where you are and where it is connected back to ground, it can be driven to the full line voltage. Basically in that case you are connected to the hot ...

54

You can't float everything without an isolation transformer - the neutral will be connected to ground at the entry into the building. For safety any class I equipment does need to remain grounded, in my lab I have an isolation transformer only for the equipment under test, the scope and power supplies still have the case grounds, and are tolerant of the ...

53

Advantages of relays over triacs: Very little voltage drop when on. This means they don't dissipate much power. For high power devices, the cost of dealing with the heat often outweighs the cost of the component that dissipates the heat. Good isolation. The relay coil is inherently electrically separated from the relay switch. Making that isolation ...

52

Customer service power lines are typically segmented into blocks or rings, so that damage to part of the grid does not disable a huge geographic region. A substation may feed several separate customer grids near it from a large regional power line. Each customer grid has its own circuit breakers at the substation, which are usually outfitted with automatic ...

48

There are four reasons for grounding the neutral. 1. Grounding neutral provides a common reference for all things plugged into the power system. That makes connections between devices safe(r). 2. Without a ground, static electricity will build up to the point where arcing will occur in the switchgear causing significant loss in transmitted power, ...

42

The Fire Dept is wrong - it is perfectly normal to plug a device with a 2-pin plug into a 3-hole socket. Breaking the ground pin off a 3-pin plug, then plugging that into a 2-hole or 3-hole socket may produce an electrical hazard - possibility of a shock. If a high-current load, like an electric heater, was plugged into that burned outlet, and the contacts ...

40

When there's 120° between phases the sum of the voltages at any time will be zero. This means that with a balanced load no current flows in the return line (neutral). Also, if each phase is 230V with respect to the neutral (star operation), then there will be 230V $\times$ $\sqrt{3}$ = 400V between any two phases (triangle or delta operation), ...

32

You can get 8 kV rated (at several thousand amps) thyristors for use in HVDC converters. The gate is optically coupled for the obvious reasons and also because, when used in tandem on HVDC links, the gate driving speed differences between series connected thyristors is important and optical is a little bit more clear cut speed-wise: - Stack a few together ...

30

These are Interference Suppression Capacitors and have excellent properties of flame retardance, self-healing, spark killers but these are NOT intended for continuous series pulse charging as they are used in this with a Triac in a dim Halogen surge load. Although they do not come out and say this in the datasheet, my experience from similar MEX-X2 caps ...

26

Circuit breakers are not enough to protect life. Circuit breakers are there to stop the cable in the walls of your house melting and possibly catching fire – circuit breakers and fuses perform the function of stopping a fire (which of course is also very dangerous to life). For direct contact with a live AC part, in the UK we have residual current devices (...

25

I measure 1VAC and 20mV DC between ground and my radiator. I would consider that negligible. Very likely there is a connection somewhere between your radiator and ground. It might be a long path though, for example: Radiator - pipes to central heating unit - cold water pipes (does your heater also provide warm tap water?) - cold water grounding connection. ...

24

Brings back memories. not all good ones. Herewith potpourri / hodgepodge - some value. Useful online calculator covering subset of question. They say Insulation Calculator This program is based on Table 2G and Figure 2F of IEC 60950. Select the circuits that bridge the insulation to be determined by using the drop down lists. For example, a Primary ...

23

If you double-check your wiring diagram you will find that is NOT a transformer. That is a common mode choke to keep RFI from being transmitted out through the mains power cord. There is no way (with currently-known technology) to make a mains-frequency transformer that small that handles as much current as a microwave oven draws. You have seen how big the ...

22

I only have a somewhat vague understanding how the electrical grid works. I know the basics of energy production, and that the electricity comes to our homes using power lines resting upon those big supports we see everywhere. I would imagine the grid somehow splits into smaller sections like a tree whose endpoints are the final destinations, such as single ...

22

The film capacitors are made to be "self healing" which just means that when they develop a short due to abuse the area around the short gets blown away, reducing the capacitance. It appears your application has frequent transients either from within or without that exceed the design capability of the capacitors. You can try to track them down at the ...

21

Being 120 degrees apart makes the phases balanced such that power transfer at any instant is a constant. If you had phases 'closer together' as you suggest, there wouldn't be any real advantage over single phase power.

20

As an amplification of Richard Crowley's answer, I'd do this in a comment but there is no way to include a circuit diagram. Your circuit actually looks like simulate this circuit – Schematic created using CircuitLab as far as the "transformer" is concerned. As stated, it's a common-mode filter which keeps the microwave from driving noise onto the ...

20

Adding to the points of Olin's answer: If you don't need the fast switching times of semiconductor devices, relays are pretty robust and cheap, compared with the circuitry needed to implement a solid state switch capable of switching the same amount of power.

19

The insulation on the cable may not be specified for the soldering temperature, and may be damaged. The insulation is selected for electrical isolation, flexibility and thermal properties. These properties may change if the insulation is taken beyond the storage temperature limits. Damaged insulation may be considered to be non-existent insulation. The ...

19

The wiring can vary in different countries, but that looks perfectly normal. Current can't just go to ground and disappear. Think of the Earth as a very big spherical conductor. If any current does go through the ground, it will end up at the earth electrode of the supplier's transformer. So the Earth is just an alternative path in parallel with the ...

18

You could use a directly coupled power supply if the unit is completely sealed. Any part of a directly coupled supply and the circuit using its power could be floating at line voltages, so this is not something you want to do for general purpose. As long as everything is sealed in the same unit that just has a line cord coming out, then these types of ...

18

This was one of those crap Chinese-made Mains-to-USB chargers that can be purchased for as little as US$1.50. I've taken them apart, and they are bad, criminally bad. The isolation from mains to output is not taken seriously- not enough creepage distance, and in one of the samples I examined, there was debris inside that could cause a direct short if you ... 18 In some parts of Europe (I know of Germany and France), the connectors are made in a way to protect you from touching mains accidentially, even if trying hard, while working with the connector: (image is from wikimedia and public domain) This particular socket is in use in Germany. France has a slightly different format (which is not compatible with the ... 18 No, the contacts will arc across and it will likely arc to the coil as well. Very, very dangerous. A commercial relay properly rated to switch 10kVAC will probably cost in excess of$1000. There are some DIY approaches, but better suited for non-novices. You should consider switching the primary, but being an inductive load that relay may not be ...

16

It is to standardise everything on a single fixed voltage. But in practice, mains voltage isn't 230V. It is standardised at 230V +10% -6%, or 216V to 253V. Here, mains voltage measures 249V, which is on the high end of the scale - but we're on a small farm road with not many other customers. Away from home I have measured it at 233V, due to resistive losses ...

16

The design of powerlines is a complex matter, in which many decisions overlay. The Powerline Ekibastuz–Kokshetau is a relatively recent build, finished 1985. There were two more lines spawning off it, one towards Moscow which is now driven with 500 kV, the other was dismantled. It is connected to a large power plant that was built at about the same time. ...

16

By the way, Dale's answer is quite good, and I mean only to append to it. They have a system of signaling over power lines. It's not a particularly high bit rate, but it gets the job done. Many smart meters can receive or send that way. Often they can remotely turn off your power if you call them and ask them to. They can also get the meter reading that ...

14

This post is mainly about ground/earth/soil as conductor and importance of grounding for safety. Maybe it's not accurrate answer but it may be useful too. For other meanings of ground - see other answers. I think answer for your question is here: http://en.wikipedia.org/wiki/Earthing_system See TN, TN-C and TN-C-S systems. Cables you are asking ...

14

Explanation for someone who needs answer "like for 6 years old": It is possible, you can build simple circuit for LED, but don't do this. Just use old phone battery charger or some external power supply because if you wont - you need serious and robust insulation there. This is more problematic than just using power supply and some resistor. AC mains is ...

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