So is the mains really 240V CT and our 120V comes from one one of those or is it different? i.e. does 240V come from the transformer outside the residence and the then for 120V only one side being used and the neutro is from the CT and is grounded somewhere while the ground on a receptacle is grounded again but at a different point(so there could exist a potential between ground and neutral?)?
Thanks, Jon
On Jun 10, 11:52 am, "Jon Slaughter" wrote: > So is the mains really 240V CT and our 120V comes from one one of those or > is it different? i.e. does 240V come from the transformer outside the > residence and the then for 120V only one side being used and the neutro is > from the CT and is grounded somewhere while the ground on a receptacle is > grounded again but at a different point(so there could exist a potential > between ground and neutral?)? >
Yep - but in rare installations (we had one in the last building) we had 120V CT so your meter reads 60 VAC from either wire to ground. Why the 'goofy' power? We have a thousand pieces of gear with power filters. The folks who built those filters use a balanced toroidal core and capacitors from each power line (hot and neutral) to chassis ground. This causes significant ground loop currents that get into the audio and video. The proper solution is to replace all the filters but a more practical one is to use 120CT though each circuit requires a double breaker and twice the wire.
GG
One presumes you're talking of the USA.
I don't know of any other country distributing power the way the USA does.
Graham
In the U.S., 240 VCT, with the center tap grounded is the normal residential service.
The 240 volt center tapped is the secondary of the pole transformer (or on or underground distribution transformer). The center tap is usually (in my experience) grounded both at the transformer, with the under the pole and overhead ground line, and also at the fuse panel (down stream of the meter) with a ground electrode.
That ground electrode is also connected to the safety ground system in the building. The fuse or breaker panel is the only place that the neutral point of the system (the center tap) and the safety ground system are to be connected directly together.
The only potential difference there should be between the safety ground at the receptacle and the neutral at the receptacle is the load caused voltage drop across the neutral branch (from power panel to receptacle) conductor. However, during a direct fault between hot and neutral (until the over current protection opens the hot side) the neutral conductor drop may approach half of the normal hot voltage. I say, 'approach', because some of the total lone voltage will be lost in the distribution transformer impedance.
As far as I know, it's exactly the same in Canada.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
In the US, residences usually get 120-0-120 (center-tapped 240) coming in off the street. Small outlets have 3 pins 120/neutral/ground, where neutral is nominally at ground potential. Big outlets, like for clothes driers and air conditioners, get 120/120/ground, which lets them run off 240 volts, the line-to-line voltage.
Our building is wired 3-phase, 240 line-to-line, with the center tap of one side of the triangle being neutral. So we have 120 outlets, 240 single-phase outlets, and 240 3-phase outlets.
Ground and neutral are nominally equal but are sometimes a few volts apart.
John
More typical now is a four-wire circuit containing both hots, neutral, and ground. This is required by current code for devices that have both 240V and
120V loads; an example of this would be a clothes dryer, in which the heating elements are 240V but the control circuitry (and usually the motor as well) is 120V.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
I can see how that might be but certainly wasn't sure.
Given that the insulation requirements are barely any more problematic, I reckon the European (and most other countries) method of using 220-240V for all domestic use makes a lot of sense.
For example, over here, the majority of major appliances (other than very small cookers) can be run off a wall socket.
Nor do we ever have 'neutral problems' that cause the voltage to vary.
Graham
U.S., Canada, Mexico, Saudi Arabia, all of Central America, much of South America, most of the Caribbean, and a few other locales, according to this:
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
reckon the European (and
lot of sense.
I was under the impression that if you DO manage to get shocked, 240 is considerably more hazardous than 120.
small cookers) can be run
Agreed, although most appliances which need special power really should be on their own circuit anyway.
Nor do we in properly functioning wiring ...
The 'neutral problems' usually involve a high resistance in the neutral wire. If you have a high resistance in one of your wires, other items on the circuit will still see a drop in voltage ... in our case, it's just that it could be a drop or _increase_ in voltage in some cases.
Martin
Or a disconnected neutral altogether -- which is definitely a Bad Thing, in that it completes a 240V circuit through any 120V loads which happen to be in use on opposite legs of the service. That's hard on parts, and risks a fire.
And that increase is a significant hazard. If you're lucky, it will simply damage appliances by burning out transformers, blowing diodes, etc. and opening the circuit. If you're not lucky, it may overheat something and start a fire.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
The electrical code provides that 240V CAN be taken into a duplex box. The hot link between the two outlets is removed, and each one is connected to a different side of the 240V. Each outlet shares the neutral and protective ground. This is common in modern kitchens, and is useful in other places, such as an entertainment center.
Don't know if it's code or not, but you should still use a 240v duplex circuit breaker for such outlets, so that you can't turn off one outlet (say, for servicing it) without realizing that the other one is still hot.
You do use a duplex breaker. In the breaker box it just looks like a 240V circuit. Kitchen circuits MUST have 20A breakers.
Not quite. The outlet for the refrigerator is permitted to be on a 15A circuit. [Article 210.52(B)(1), Exception 2]
And there is no requirement for the kitchen lighting to be on a 20A circuit.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
I had in mind the duplex outlets provided for portable kitchen appliances, but I'll check with my attorney next time.
You're quite right that the small appliance circuits are required to be 20A. And the Code also specifies that the 20A requirement applies to *all* outlets in the kitchen, even the ones that are there to meet the "no more than 6 feet" interval required on walls. But there is that one, specific exception for "refrigeration equipment".
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
Cite, please?
--
Regards,
Doug Miller (alphageek at milmac dot com)
It\'s time to throw all their damned tea in the harbor again.
Actually, the way it's worded, you're suppose to kill the distribution panel. not just a breaker.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
If you were any electrician or close, you would know that lock and tag out is a must when working on electrical. The exception to the rule is if you have to do live testing that is required to analyze a problem. In which case, you're suppose to be warning arc flash clothing.
Now, depending on the energy level you're disconnecting, you're suppose to be wearing the arc flash clothes as a minimum to the point of wearing an arc flash hood along with a full safety jumper, gloves etc...
You should never assume your breaker to be functioning correctly and you should never assume that you know which is the correct breaker.. Normally, there is only 1 distribution center that kills it all! and even then, one should first check to ensure there isn't any leakage in which case, your main switch should be replaced.
Below 50 Volts does not fallow these strict rules.
This is for the USA, I don't know about other places.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.