Voltage drop

[augie47]

Taking into account that the NEC directly addresses voltage drop as a non-enforceable FPN, I've been asked for my opinion on a situation.
Without given a specific load or specific wire size, if a job (industrial) calls for a circuit to feed 120v receptacles at various locations is there any "accepted standard" where a certain maximum voltage drop would be mandated ?
Specifically a plant asked for a 20 amp circuit with convenience outlets at various locations and are now concerned that with a 12 amp load the voltage drop is excessive for items being plugged in.
If the job consisted of ONE duplex as opposed to multiple outlets, would that make a difference ?
My opinion is that, without specifying a load, the calculated load of 180va would be all that would be applicable to the E/C.

 

[skeshesh]

I pretty much agree with your opinion from an inspector's prospective.

Unless you see a specific unit/machine/etc. plugged into a receptacle during inspection, it is not your responsibility to spend time and effort to dig deeper. Of course, if you find, either on documents or in the field, a situation where the circuit may be overloaded you should flag it. In the case you describe, the designer may have made an error and allowed for excessive voltage drop which is unfortunate but as you pointed out is referenced in a FPN.

That being said, I still think it's kind of you to bring it up and I would certainly want to know about this possible flaw (even if it's just an opinion) if I were the owner.

As far as an "accepted standard" I've always seen 120V circuits be designed to no less than %10 VD (often less than that). But again, there's a big difference between standards and regulatory code.

 

[cpal]

Taking into account that the NEC directly addresses voltage drop as a non-enforceable FPN, I've been asked for my opinion on a situation.

If your requested opinion is directed towards code compliance, then I agree that the Informational Notes's are not enforceable and beyond the purview of the AHJ. If you have been asked for a design consult then I would recommend compensating for anticipated Vd.

 

[augie47]

It was more a "point of conversation" at a facility where I am inspecting.
Some personnel are concerned about the voltage drop problem and were approaching it as a Code issue. My contention was that as far as the NEC was concerned, voltage drop was not enforceable.
They wrere of the opinion that there was a requirement (NEC or otherwise) that a 20 amp circuit to an outlet must be required to operate a 16 amp laod within certain voltage drop peramaeters.
I told them I knew of not such requirement other than specific jobs specs.

 

[cpal]

Both you and I are of a like mind

 

[defears]

While everyone knows it's not enforceable you only know your plant and what could be used on them. If I don't know any real loads I just use #10 up to 500 feet and ask how much they want to spend on anything longer. Managers only remember when things don't work, not when they do.

 

[Dennis Alwon]

As an EC if I ran a 20 amp circuit and wasn't sure of the load then I would make sure it would carry 20 amps. Maybe cheat a bit if I knew the loads were incandescent lights.

 

[hurk27]

I think the closest you could come to if the load is known such as office printer and copiers, would be 110.3 but the load would have to be there when you inspect, and the listed instructions would have to directly require a certain VD limit, but other wise its a hard call, for the most part the only things I know of that have a problem with VD is motor loads, motors can stall and cause damage to them if there is voltage drop, especially high torque applications like air compressors, AC units, most electronic appliances have very little problems with voltage drop, network items can have a problem with voltage drop on the neutral but that is because of poor designs in this area and we hear about it when we get called to solve a problem with a differential voltage between the neutral and grounding, but for the most part VD on most things rarely cause problems just annoyances when the lights dim.

 

[chris kennedy]

Without given a specific load or specific wire size, if a job (industrial) calls for a circuit to feed 120v receptacles at various locations is there any "accepted standard" where a certain maximum voltage drop would be mandated ?

The EE doesn't list this on the approved drawings?

My opinion is that, without specifying a load, the calculated load of 180va would be all that would be applicable to the E/C.

We have a requirement here in the Florida Building Code, note the phrase "design load".

13-413.ABC.1.2 Branch circuits. Branch circuit conductors
shall be sized for a maximum voltage drop of 3
percent at design load.

 

[augie47]

The EE doesn't list this on the approved drawings?".

The dwgs. call for increased wire sizes at certain lengths. Unfortunately not to the point of eliminating the problem.
It's a spitting contest

We have a requirement here in the Florida Building Code, note the phrase "design load".

Thanks

 

[Crionics]

The dwgs. call for increased wire sizes at certain lengths. Unfortunately not to the point of eliminating the problem.
It's a spitting contest

Thanks

I don't always increase wire sizes to strictly adhere to the FPN's for VD...this is where the EE must understand what is equipment will be supplied and what it's tolerances are. I used to work at an MEP firm designing the occasional MRI, which has extremely tight VD requirements. Now I design refinery revamps where I may have to take a 480V circuit 800 feet, and sizing a 20A circuit with #2 wire is a little rediculous for some applications. The engineer must always use discretion and understand what the situation calls for.

 

[steve66]

They know they have a 12 amp load, so it seems like these receptacles were for a specific device. But the only place you can really go from there is the manufacturers instructions for whatever they a plugging in. If it has a minimum voltage listed, you could require that be present at the receptacle when the device is running. But I think that's really a stretch.

And even if you do that, they can still plug in a 100', 18ga extension cord at the farthest outlet, and then the device still won't have the voltage it needs.

 

[mivey]

As an EC if I ran a 20 amp circuit and wasn't sure of the load then I would make sure it would carry 20 amps. Maybe cheat a bit if I knew the loads were incandescent lights.

That is how I do it. I make exceptions for outlets to specific things like condensate pumps, etc.

 

[gar]

110105-1035 EST

A different view not related to code.

From an equipment design perspective I have have always used the criteria that what I am designing should work from at least 95 to 135 V input steady state, and its even better to go somewhat closer to 85 for the lower limit. Part of this below 95 V criteria would be the assumption that the dip duration is at most 1 or 2 seconds and thus size the power supply capacitors to ride thru this below 95 dip. This is to account for momentary loads that may cause substantial voltage dips. I do not want to be measuring something and have an error in the measurement because of a momentary voltage dip.

If I am defining the supply side and I have a general purpose 20 A circuit, then to determine wire size I would calculate voltage drop at 100 A and not want to drop below about 105 at the most remote point of the circuit. If the nominal supply voltage was 120 V, then the result for loop resistance is (120-105)/100 = 0.15 ohms. For a 100 ft distance the loop is 200 ft and #10 copper would be a little over at 0.2 ohms, but would be a satisfactory choice. For less sever momentary loads #12 would be fine.

If you have equipment that has narrow voltage limits, then use a Sola, or other means to solve the problem at the equipment. Maybe buy different equipment with greater voltage tolerance.

.

 

[charlie b]

. . . with convenience outlets at various locations. . . .

When I perform a design that includes this concept, I calculate the load at 180 VA per duplex receptacle, and I don't generally perform a voltage drop calculation. That is because I don't think it is necessary, and because I generally keep the distances (panel to farthest outlet) shorter than 100 feet.

If the owner has a concern that a 12 amp load might not have sufficient voltage to operate properly, then the owner is free to pay the extra needed to increase the wire size, to provide more panels throughout the facility so that the circuit runs are shorter, or to have detailed voltage drop calculations performed to demonstrate that their desired minimum voltage would be available. This is not a code issue, and the code cannot be used to compel the EC to pay for any upgrades.

 

[augie47]

thanks charlie b and others. that (charlie's) response was basically mine...