What's the rationale for 277v not being permissible in dwelling areas?

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Electric-Light

Senior Member
I recall it had something to do with restrictions on voltage respect to ground of any conductor. In the US, residential wiring does not exceed 120v nominal even on 240v circuits as it is center tapped.

This includes lighting in individual units in large apartment complexes, dormitory etc.

There's not a whole lot of difference between 480Y/277 vs 415Y/240. Every receptacle in just about anywhere outside of North America has the hot conductor 240v floating above ground and they don't really have issues.
 

iwire

Moderator
Staff member
Location
Massachusetts
We have the lower voltage readily available and it seems that shocks would be less severe with 120 vs 277.

Take it from a guy that has experienced both more than a few times.:ashamed1:

120 is bothersome, it hurts a bit.

277 is like getting kicked by a mule, it ain't fun, you don't really laugh it off.

When 120 faults to ground it makes an arc, it does a little bit of damage.

When 277 faults to ground it is (in my experience) much more spectacular and damaging, blowing holes through the walls of enclosures etc.
 

SEO

Senior Member
Location
Michigan
Using 277V squared =76729 divided by 500 ohms resistance =153.46 watts.

Using 120V squared=14400 divided by 500 ohms resistance =28.80 watts.

153.46 divided by 28.80 =5.33.

277 has aprox 5 times the cooking power than 120. I used 500 ohms for a person .
 

Electric-Light

Senior Member
Well, they've been using 240v anywhere but North America and hasn't been much of an issue, has it? 240v L-N isn't that much less than 277v. L-N
If the brits can handle it, why can't we?
 

iwire

Moderator
Staff member
Location
Massachusetts
Well, they've been using 240v anywhere but North America and hasn't been much of an issue, has it? 240v L-N isn't that much less than 277v. L-N
If the brits can handle it, why can't we?

What reason should we when 120 is readily available?

It has been shown above that it brings more destructive power to the table and what hardship is being caused by limiting it's use in dwelling units?
 

kbsparky

Senior Member
Location
Delmarva, USA
...If the brits can handle it, why can't we?

They can't. They have changed their rules regarding using temp power on their construction sites. They are moving towards requiring the use of 110 Volt tools, to minimize lethal shock hazards associated with jobsites' use.

They call it a "reduced low voltage system," where a transformer is used to feed the 110 volt circuits, with a grounded center-tap. This reduces the available potential to ground to approx. 55 volts.

Here is some useful information about this aspect.
 

Electric-Light

Senior Member
They can't. They have changed their rules regarding using temp power on their construction sites. They are moving towards requiring the use of 110 Volt tools, to minimize lethal shock hazards associated with jobsites' use.

They call it a "reduced low voltage system," where a transformer is used to feed the 110 volt circuits, with a grounded center-tap. This reduces the available potential to ground to approx. 55 volts.

Here is some useful information about this aspect.

That's for special application that only applies to construction sites. Household outlets are still 240v L-N.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
We have the lower voltage readily available and it seems that shocks would be less severe with 120 vs 277.

Take it from a guy that has experienced both more than a few times.:ashamed1:

120 is bothersome, it hurts a bit.

277 is like getting kicked by a mule, it ain't fun, you don't really laugh it off.

When 120 faults to ground it makes an arc, it does a little bit of damage.

When 277 faults to ground it is (in my experience) much more spectacular and damaging, blowing holes through the walls of enclosures etc.
I have to agree with Iwire on all counts!
I've tasted copper after getting hit by 277 and when you cut a hot wire while your pliers are touching ground..... You're gonna stand still for a bit...at least till you can see again!
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
What's the rationale for 277v not being permissible in dwelling areas?

I always thought that is was to keep sparky's from taking 277 volt fixtures home, similar to left handed lamps. ;)

Actually IMO it's all about safety and cheaper filaments on incandescent lamps.
 

sgunsel

Senior Member
Regardless of merit, after 100+ years the installed base of wiring, motors, appliances and such would make it economically and practically foolhardy to attempt any major conversion. Half of Japan is on 50 Hz, the other half on 60 Hz. The cost, aggravation, and hazards of attempting to convert are simply too great once established. We still have some odd systems in this country "because they are" and it is cheaper to maintain than to attempt switching over. Some old buildings in Cleveland only converted from DC to AC in the 50's (some of the old switchgear was abaondoned in place and is pretty fascinating).
 

Besoeker

Senior Member
Location
UK
Well, they've been using 240v anywhere but North America and hasn't been much of an issue, has it? 240v L-N isn't that much less than 277v. L-N
If the brits can handle it, why can't we?
We Brits generally have a very much simpler system.
LV is nominally 400V line to line and 230V line to neutral derived from the 400V.
Local distribution transformers are usually 11kV delta primary and 400V star (wye) 3-ph + N secondary. Domestic supplies are 230V and all domestic equipment runs at that voltage. Lighting, televisions, computers, water heaters, washing machines...
No 480, no 277, no 120, no high leg delta.
Just 230V for domestic.
Commercial/light industrial premises might have a three phase for wire supply.
Office equipment is 230V and taken from phase to neutral of that supply.
Some production machinery uses the three phase supply to power various motors for presses and turning machines.
 

Besoeker

Senior Member
Location
UK
Regardless of merit, after 100+ years the installed base of wiring, motors, appliances and such would make it economically and practically foolhardy to attempt any major conversion. Half of Japan is on 50 Hz, the other half on 60 Hz. The cost, aggravation, and hazards of attempting to convert are simply too great once established. We still have some odd systems in this country "because they are" and it is cheaper to maintain than to attempt switching over. Some old buildings in Cleveland only converted from DC to AC in the 50's (some of the old switchgear was abaondoned in place and is pretty fascinating).
Valid points.
You work with what you have even if it isn't optimum.
 

Electric-Light

Senior Member
Regardless of merit, after 100+ years the installed base of wiring, motors, appliances and such would make it economically and practically foolhardy to attempt any major conversion. Half of Japan is on 50 Hz, the other half on 60 Hz.

Some of elevators in NYC were DC. Con Edison discontinued the service in 2007, so it can be done.

Japan also has a unique voltage. 100v for everyday home stuff, 200 for larger stuff in home. Light industrial is 200v 3 ph delta. Corner ground or 100/200/173 wild leg. I don't think wye is common there.
 

norcal

Senior Member
I did come across 277V lighting in a dwelling once, bootleg MIL unit in a shop w/ a 480Y/277 service, recycled 277V troffers in the kitchen & living room that the owners were attempting to replace w/ ceiling fans, long story but 277 is no longer in the home.

Here are the panels for the bldg.

DSC03080.jpg


DSC03079.jpg


They are a good example of how not to do things.
 

iwire

Moderator
Staff member
Location
Massachusetts
We Brits generally have a very much simpler system.

In my personal opinion the above is simply an opinion not a fact.

I find having choices makes things easier. You can choose the proper voltage for the task at hand instead of trying to work around a 'one size fits all approach' which is rarely optimal. In most of the buildings I work in I can choose 480, 277, 208 & 120. For things that come in direct contact with people 120 is often chosen. For example say the lighting in a supermarket or other store that is down low with the customers will typically be 120 volt on the other hand the lighting on the ceiling out of reach will be 277 or 480 so we can run a lot of lights and distances without voltage drop being a factor to worry about.

And we just keep adding voltages, lighting systems under 30 volts are becoming much more common.

My point is if you are used to having multiple voltages it is not complicated, it is helpful.:)
 

knoppdude

Senior Member
Location
Sacramento,ca
Hundreds of billions would have to be spent on new equipment and appliances that could handle the change in voltage, as well as new electrical systems installed. Perhaps this is a good idea.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Every receptacle in just about anywhere outside of North America has the hot conductor 240v floating above ground and they don't really have issues.

Of course they have issues. They have accidents and people get shocked and sometimes killed just like what happens here. The real question is do more people get shocked and killed due to the higher voltage? Have you done any research on this before saying "they don't have issues."??

Every receptacle in just about anywhere outside of North America has the hot conductor 240v floating above ground....

Japan also has a unique voltage. 100v for everyday home stuff....

I guess just about anywhere doesn't include Japan????
 

Besoeker

Senior Member
Location
UK
In my personal opinion the above is simply an opinion not a fact.

I find having choices makes things easier. You can choose the proper voltage for the task at hand instead of trying to work around a 'one size fits all approach' which is rarely optimal. In most of the buildings I work in I can choose 480, 277, 208 & 120. For things that come in direct contact with people 120 is often chosen. For example say the lighting in a supermarket or other store that is down low with the customers will typically be 120 volt on the other hand the lighting on the ceiling out of reach will be 277 or 480 so we can run a lot of lights and distances without voltage drop being a factor to worry about.

And we just keep adding voltages, lighting systems under 30 volts are becoming much more common.

My point is if you are used to having multiple voltages it is not complicated, it is helpful.:)

It might not entirely surprise you that I totally disagree.:p
No live electrical part should come in contact with people.
If a supermarket let that happen they would be under immediate investigation,and the management would probably face criminal proceedings
And 120V isn't exactly a safe voltage anyway.
For most residences the ONLY supply coming into the premises is 230Vac single phase. Plugs an sockets are all the same. The live an neutral prongs are disconnected before any conductive part is exposed. When the third pin, the earth (ground) is withdrawn, a shutter closes off access to the live and neutral. Your children or grandchildren can't poke stuff into them.
And we don't have 120-0-120 systems so the issue of a loose neutral potentially sticking up to 240V on an an appliance rated at 120V just isn't an issue. Actually, there is no potential for connecting anything to the wrong voltage with a resulting flash and a bang - or worse.

No, it isn't a work around for the task in hand. It is just an elegantly simple system that accomplishes all the tasks required of it.

:D
 
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