Sure Andrew.
In the US we have two phase power to every house. Even in the UK the phase to your house shares a neutral with another phase that provides service to other customers.
So the service to my house has three wires; 120 V, 0 (the neutral), and 120 V. There is 240 V across the two "hot" wires since they're out of phase.
Now the neutral wire has some small resistance so if a current flows through it there will be a small voltage across it. If both phases have identical current then the current through the neutral will be zero. If one phase had 10 amps and the other phase has 5 amps then 5 amps flows through the neutral; the voltage drop on the neutral wire will be in phase with the 10 amp phase. It's KCL. So if the voltage is pulled down on one phase, it will be pulled up on the other phase. That's KVL.
Imagine if the neutral were open. If a 1000 watt toaster was running off one phase and a 100 watt lamp was running off another phase, they would be in series. Which device would have more voltage across it?
When I power up the air compressor in my shop (150 amp surge to start), the lights get brighter for a moment. That is because the air compressor is on one phase and the lights are on another phase. The voltage on one phase surges when the voltage on the other phase sags. and you can clearly see it in the lights. That's simple KVL.
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Yes, the usual suspects again. Amp diagnosis over the internet by looking at the calender.
If you don't replace every other electrolytic cap in the amp at this time, you'll get to visit your amp repairman again soon, and again over and over again. If he replaced just one or two e-caps the others are too old. For like new reliability, replace all e-caps at the 20 year boundary or when the first goes bad, and probably replace the volume control and clean the protection relay contacts, too.
The US supplies a single phase to your house via a centre tapped secondary.
That is very different from 3phase.
I know exactly what what 3 phase is.
Single phase fed through a center tapped secondary is two phase. The two hot wires are 180 degrees out of phase, and individual circuits are tapped from hot to neutral. Central air conditioners are typically fed off the two hot wires that provide 240 volts. The configuration is versatile like that. You can even wire a UK 240 volt outlet to the service of my house; you see this in some hotels - no plug in transformer is needed to run European devices.
KVL and KCL are universal laws. They apply to single phase, two phase, or 3 phase. I hope you understand my explanation of voltage fluctuation in the phases. It applies to 3 phase too, whether it is a delta or wye configuration. (Delta is with no neutral; wye is with a neutral.) It very well understood in my industry and easily observable.
240 volts center tapped is still called single phase. It is fed from ONE phase of the distribution system. If you get a fault on one of the other phases a mile away, BOTH sides of your 240 go up not just one. So it can take out your A/C, not just your stereo.
Once you're downstream of the pole transformer, an overload or fault on one pole (not phase) will cause the other to go up. How about a nice open neutral back at the pole? Both you and your neighbors get to experience lights going up and down with no apparent explanation. Stoves, water heaters and AC's continue to function normally. And good luck convincing the power company that anything is wrong.
Once you're downstream of the pole transformer, an overload or fault on one pole (not phase) will cause the other to go up. How about a nice open neutral back at the pole? Both you and your neighbors get to experience lights going up and down with no apparent explanation. Stoves, water heaters and AC's continue to function normally. And good luck convincing the power company that anything is wrong.
From an engineering point of view, it is two phases. But technically you're correct. It starts out as one phase from the distribution system.
I did this for a living and you are arguing semantics.
Absolutely true.
If one pole goes out, the other pole will still supply power. If one pole is overloaded, the other will go up which is the point I'm trying to make. However if a neutral goes out
So all we're arguing is semantics.
Not true at all. If you communicate the problem to them correctly (not just "my lights are too bright") they'll come right out, right away, 24/7. I've had to call them myself.
An open neutral is the worst scenario.
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Apparently, your techs were better than mine. It took four separate complaints about fluctuating voltage before they finally decided to look beyond our service entrance and found it on the POLE. They must have been afraid of heights or something.
I would have already known what was wrong before calling them. A quick check of the service box with a voltmeter and visual check of the service wires is all that's required.
For the benefit of those not versed in power distribution systems, the neutral and ground are connected together inside your service box, but are kept separate throughout the distribution system inside your house. So the neutral goes to ground; but it is referred to as the "designated conductor". The neutral is never fused; so if you screw up the phasing of your wiring, you have created a grave hazard.
There's an old saying of electricians-two wires, hook em up; three wires, f--- em up. That's all you need to know to be an electrician.
There's an old saying of electricians-two wires, hook em up; three wires, f--- em up. That's all you need to know to be an electrician.
It gets complicated in the UK. A lot of modern estates now have a TN-C-S system (protective multiple earth) where there is a combined neutral and earth on the property. This is the case in my property - at my service box (well, the cupboard under the stairs!), the protective earths are connected to the Neutral from the supply cable.
There are also plenty of houses using a TT system, where protective earth is local to the property e.g. a buried ground rod. This is typical of very old houses where electricity was installed later - I lived in a property where the power was carried by two thick cables running across the front of the houses.
Also, there are properties using TN-S, where the earth is supplied by the power company, usually via the steel armour shielding of the supply cable
DIY and Home Improvement Wiki - Electrics - Earthing supply types and bonding - Earthing arrangements
It's not common to see "pole pigs" in the UK, at least not as common as it is in the US. Typically they are seen in more rural areas.
There are also plenty of houses using a TT system, where protective earth is local to the property e.g. a buried ground rod. This is typical of very old houses where electricity was installed later - I lived in a property where the power was carried by two thick cables running across the front of the houses.
Also, there are properties using TN-S, where the earth is supplied by the power company, usually via the steel armour shielding of the supply cable
DIY and Home Improvement Wiki - Electrics - Earthing supply types and bonding - Earthing arrangements
It's not common to see "pole pigs" in the UK, at least not as common as it is in the US. Typically they are seen in more rural areas.
Thanks for that jaycee.
I maintain that the safest system is the one that is grounded locally. All (compliant) services in the US are grounded locally. The neutral wire is also grounded at the utility pole. With a configuration like that, there can be significant voltage differential between neutral and ground without a local ground. It is essential that the neutral be as close to zero volts (true ground) as practical, for safety reasons.
I maintain that the safest system is the one that is grounded locally. All (compliant) services in the US are grounded locally. The neutral wire is also grounded at the utility pole. With a configuration like that, there can be significant voltage differential between neutral and ground without a local ground. It is essential that the neutral be as close to zero volts (true ground) as practical, for safety reasons.
Fast Eddie D is correct in the current draw being able to cause higher voltage on the opposite leg.
A residence 300 or 400 feet from the pole transformer can get the sag/surge as he stated.
Here in NY, the power company responds VERY quickly to a call stating the loss of a neutral. I spotted one up at the tap which fed a building, walked in and spoke to the business owner, I was walking to a restaurant for dinner.
Turned out she was having issues with billing which seemed excessive. I asked her if she noticed the lights dimming or getting brighter...she said yes, both.
I told her to call immediately, she knew the number by heart after many many attempts.
She started getting the same runaround, so I asked to speak to the rep on the line. I told the rep..."The neutral to this building is completely disconnected up at the line taps, I cannot access the basement to determine the health of the bonding to the water feed pipe (if any), the lights here are both dimming and getting too bright depending on the transient loading in the building. This is an electrocution problem. Please send a truck out immediately."
I had dinner, and walked back 45 minutes later.
The truck had come, fixed it, and left in under half an hour. Sometimes it pays to know the buzz words..
Get this: The woman's husband was a plumber. When she told him the story, he told her to thank me, this is a seriously dangerous issue should a plumber ever have to work on a copper system. Plumbers have been electrocuted by that scenario.
My apologies for repeating this story, I believe it justified however.
jn
Sometimes it pays to know the buzz words..
Exactly.
Indeed.
Plumbers sometimes screw up grounding systems too. I've seen it personally.
Never, never, never, never, never unhook the ground line (or remove the pipe that it grounds to) without first turning off the main breaker (or removing the meter). Never!
In the UK, using a cold water pipe as a earth rod is an old practice - but one which is now banned. If a local earth is present (such as in a TT system) it must be a dedicated earthing rod.
Also here, only a single phase is ever delivered to a domestic property. Typically a housing estate's load is spread over the three phases. A broken neutral therefore would typically cause complete loss of supply.
Also here, only a single phase is ever delivered to a domestic property. Typically a housing estate's load is spread over the three phases. A broken neutral therefore would typically cause complete loss of supply.
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