Tolerance on 120V and 240V Electrical Outlets

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jackie_chad

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Hello everyone,

I am an electrical engineering student and have been searching out an answer to this question for several days. Could someone please tell me the tolerances on a 120V and 240V outlet in a residential home. I have seen +/-5% and +/-10%, along with other numbers throughout my search. Is there a standard that dictates what these voltage tolerances are?

Thank you for your time.
 
Thanks, iwire. I believe this is what I was looking for. I noticed this paper is from 1999. Do you know of anything that has come out more recently on Voltage Tolerances?
 
The voltage AT THE SERVICE should vary by no more than 5% either way, for most types of service in the USA.
The voltage at the outlet will be lower than that at the service due to voltage drop within the installation.

Code does not specify what voltage drop is acceptable, though a maximum of 3% is a widely accepted figure it is not actually a requirement.

Presuming a 3% drop in the conumers installation, then the voltage at the outlet could vary from 92% of nominal up to 105%.

Tolerances vary in different countries, in the UK it is from 94% up to 110% of nominal at the service, or from 217 volts up to 253 volts for a nominal 230 volt service.
Voltage at the outlet could be as high as 256 volts (253 + about 1% voltage rise due to grid tied PV) or as low as 205 volts with the service at 217 volts and about 5% drop in the consumers installation.
In parts of Europe anything between 200 and 260 at the service is good.
 
Also note that most people use the same receptacles for 240V and 208V. So one major difference, if you've measured a given voltage at a receptacle, is what is even being provided. You can't tell by looking at the receptacles.
 
jackie_chad said:
Thanks, iwire. I believe this is what I was looking for. I noticed this paper is from 1999. Do you know of anything that has come out more recently on Voltage Tolerances?
Click to expand...

No I do not know of anything more recent.

It is not the kind of thing that changes often, that would be rough on older equipment.
 
broadgage said:
The voltage AT THE SERVICE should vary by no more than 5% either way, for most types of service in the USA.
The voltage at the outlet will be lower than that at the service due to voltage drop within the installation.

Code does not specify what voltage drop is acceptable, though a maximum of 3% is a widely accepted figure it is not actually a requirement.

Presuming a 3% drop in the conumers installation, then the voltage at the outlet could vary from 92% of nominal up to 105%.
Click to expand...

Here is what the NEC suggests, as you noted it is not a requiment.

Informational Note No. 2: Conductors for feeders as defined
in Article 100, sized to prevent a voltage drop exceeding
3 percent at the farthest outlet of power, heating, and
lighting loads, or combinations of such loads, and where
the maximum total voltage drop on both feeders and branch
circuits to the farthest outlet does not exceed 5 percent, will
provide reasonable efficiency of operation.
Click to expand...

So 3% max VD on the feeder, 2% additional on the branch circuit for a total of 5% VD from the service point.

ANSIC841.jpg
 
iwire said:
Here is what the NEC suggests, as you noted it is not a requiment.
So 3% max VD on the feeder, 2% additional on the branch circuit for a total of 5% VD from the service point.
Click to expand...

But if you meet 1% on the feeder you then have an additional 4% on the branch circuits.
There are several design alternatives, and it may be more cost effective to go well beyond the requirement on the feeders and have more flexibility for long branch runs.
The branch runs will often add up to more copper weight than the feeders.

The existing language of the recommendation should not be interpreted as a blanket 2% limit (suggested) on the branch circuits. It does not say that.
 
GoldDigger said:
But if you meet 1% on the feeder you then have an additional 4% on the branch circuits.
There are several design alternatives, and it may be more cost effective to go well beyond the requirement on the feeders and have more flexibility for long branch runs.
The branch runs will often add up to more copper weight than the feeders.

The existing language of the recommendation should not be interpreted as a blanket 2% limit (suggested) on the branch circuits. It does not say that.
Click to expand...

:D

Thank you Captain obvious.
 
jackie_chad said:
Hello everyone,

I am an electrical engineering student and have been searching out an answer to this question for several days. Could someone please tell me the tolerances on a 120V and 240V outlet in a residential home. I have seen +/-5% and +/-10%, along with other numbers throughout my search. Is there a standard that dictates what these voltage tolerances are?

Thank you for your time.
Click to expand...

In my neck of the woods, the law mandates the poco supply voltage at minus 10% to plus 10% of the contracted voltage.
 
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