You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter hh76
- Start date

- Status
- Not open for further replies.

- Location
- Seattle, WA

- Occupation
- Electrical Engineer

I agree with the 1%, and I confirm the estimate of 95 feet.

- Location
- New Milford, CT

Permited voltage drop for a 240 volt circuit is 7.2 volts.

Permited voltage drop for a 240 volt circuit is 7.2 volts.

Not to be the CODE police but voltage drop is a

- Location
- Wilmington, NC

in this case the design perameters call for a 1.5% drop or less.

can anyone point to something in writing that could help to argue my case?

What are you trying to argue, that the VD is for 240-volt and not 120-volt?

If this is a straight 240-volt circuit, I think that fact would be the supporting fact. If it's a 120/240-volt circuit, then with a 1.5% limitation and someone was using it at 120-volts then you would exceed the 1.5% limitation.

Your OP did not indicate a 120/240-volt circuit, so I'd say you meet the design parameters.

- Location
- NE Nebraska

240v 1ph circuit 16.7amps

using 8awg I get a drop of 2.5v

Is that 2% based on 120v from each conductor to ground, or 1% of 240v.

not sure what you are trying to ask 2% of 120 and 1% of 240 are the same thing.

- Location
- NE Nebraska

It will be based on the voltage on the load and/or net load. If the 16.7 amps made up of a bunch of 120 volt loads, you will need to do a 120 volt calc for the worst unbalanced case.When somebody needs that in terms of % drop, do I use 240v, or 120v?

If it is 16.7 amps of 240 volt loads, the drop is a % of 240 volts.

- Location
- Wilmington, NC

I understand that 2% of 240 is the same as 1% of 120.

When I run calculations I get a 2.5v drop. When somebody needs that in terms of % drop, do I use 240v, or 120v?

It is a 120/240v circuit.

Now it gets a little dicey. If you have loads on both phases, the VD drop acts like a 240v circuit and the % is split between the 2 loads. The VD drop will split between the 2 loads. If you have 16.7 amps on each phase, then the VD will be 2.5v on the overall circuit and each phase will see 1.25v drop (it acts like a series circuit since the neutral is carrying 0-amps).

If you had 16.7-amps on A phase and 8.35-amps on B phase then the VD for 8.35-amps is split between the 2 phases and the VD drop for the additional 8.35-amps for A phase will be seen by A phase only. VD for 8.35-amps is 1.25v /2 = .625VD on A and .625VD on B. Now we need to add the 2nd 1.25VD (for the rest of A's load) to A only (since B's total load has been accounted for) for a total VD on A of 1.875-amps.

Now if B was turned off and A left on, A's VD would go up to 2.5V since B is not loaded.

(Sorry I couldn't give you a more clear explanation, I never went to school for this and don't know how it's taught).

- Location
- New Milford, CT

Not to be the CODE police but voltage drop is arecommendationper 210.19(1) ex. 2FPNper 90.5(C).

FPN. Good point.

- Location
- Albuquerque, NM

Permited voltage drop for a 240 volt circuit is 7.2 volts.

Ouch here in NM the allowed drop on a 240 circuit is 5 volts. PNM comes running anytime I call and report over or under of 5 volts or more

Has to be exactly 5 volts? That is tough. :grin:...anytime I call and reportover or underof 5 volts or more

But, if the 2.5V you measure across the wire only, you obviously don?t know what's the nominal is, since the load can be connected as 120 or 240 using the same wire. So, in that case you better do not use % term with reference to that drop.

Pol

You should because that will determine the current value and which impedance it flows though.you obviously don?t know what's the nominal is, since the load can be connected as 120 or 240 using the same wire. So, in that case you better do not use % term with reference to that drop.

You can calculate in per unit current as well. For distribution systems, one method I use is per unit currents, voltages, and impedances. I only convert back to volts and amps at the end if I need it.

... but I've got an engineer sizing wire based on the voltage for the individual conductor.

in this case the design perameters call for a 1.5% drop or less.

A 1.5% voltage drop based on the individual conductors is the same as saying an allowable 3% VD for a total length of a 2-wire circuit, but disallows any "improvements" as a result of balanced 1? 3-wire circuit (i.e. 120/240), or a balanced 3? 4-wire circuit (e.g. 208/120 or 480/277).

In the case of a 240V 1? 2-wire circuit, your circuit total VD is 50% per conductor.

Last edited:

- Location
- Seattle, WA

- Occupation
- Electrical Engineer

- Status
- Not open for further replies.