Voltage Drop - Design Phase

[Rock86]

I am being asked by a 3rd party code review team to "Revise construction documents as required to document the total voltage drop across the combination of feeders and branch circuits (drop cannot exceed 5 percent). Refer to ECCCNYS Section C405.9." The project is typical Fire House, no significantly long runs. I don't typically perform voltage drop calculations for a typical building. Has anyone had to comply with this during design phase or prior to construction phase?

 

[infinity]

For a small footprint building with short runs it sounds like a waste of time.

 

[ron]

It has happened to me a few times. The Energy Code is the only voltage drop code, and I suspect will be enforced more often.

I modeled all feeders and the worst case branch for each.

 

[augie47]

It has happened to me a few times. The Energy Code is the only voltage drop code, and I suspect will be enforced more often.

I modeled all feeders and the worst case branch for each.

We have not had to address that as of now. Curious on a general purpose branch circuit what value do you use for the load ? The overcurrent device rating ?

 

[Rock86]

It has happened to me a few times. The Energy Code is the only voltage drop code, and I suspect will be enforced more often.

I modeled all feeders and the worst case branch for each.

Ouch. I guess I will have my work cut out for me.

I know there is an AutoCAD MEP which does voltage drop calculations base on the generated circuit lengths. If this continues, I may need to consider investing in that.

 

[Rock86]

We have not had to address that as of now. Curious on a general purpose branch circuit what value do you use for the load ? The overcurrent device rating ?

I would use the connected load. General receptacles at 180VA, lights at their load, dedicated circuits at their rated load.

 

[ramsy]

Curious on a general purpose branch circuit what value do you use for the load ?

180W is most likely used per GP load calcs.

By de facto 1500W space heaters are being used by the office workers.

 

[ron]

I would use the connected load. General receptacles at 180VA, lights at their load, dedicated circuits at their rated load.

This is what we do. Revit calculates it based on the breaker size and connected load, choose wisely what you display.

 

[Rock86]

This is what we do. Revit calculates it based on the breaker size and connected load, choose wisely what you display.

Yes, Revit is nice for that. Have you used ACAD MEP?

 

[ron]

Yes, Revit is nice for that. Have you used ACAD MEP?

Nope, went from AutoCAD to Revit, nothing in between

 

[gene6]

The Energy Code is the only voltage drop code

Voltage drop was actually never removed from the NYC Electrical code, it goes back decades to when it was still in the NEC.
Here is the NYC code amendment:

SECTION 210.19
Subsection 210.19(A)(1) – Add a new sentence at the end of the paragraph before the first Exception to
read as follows:
Conductors of branch circuits shall be sized to allow for a maximum voltage drop of 3 percent at the last
outlet supplying light, heat or power and the maximum voltage drop allowable for feeders and branch
circuit combined shall not exceed 5 percent.
FPN No. 4 – Delete the FPN in its entirety.

NYC code requires a lot of specific things like dedicated circuits for plug in AC units, and #14 is not allowed as a wire size.

 

[ron]

Voltage drop was actually never removed from the NYC Electrical code, it goes back decades to when it was still in the NEC.
Here is the NYC code amendment:

NYC code requires a lot of specific things like dedicated circuits for plug in AC units, and #14 is not allowed as a wire size.

The difference being that I have never been asked by the NYC Dept of Buildings to provide a voltage drop calculation, as I have been for seevral other jurisdictions in the country based on the adopted Energy Code.

NYC will always be an outlier.

 

[Rock86]

Voltage drop was actually never removed from the NYC Electrical code, it goes back decades to when it was still in the NEC.
Here is the NYC code amendment:

NYC code requires a lot of specific things like dedicated circuits for plug in AC units, and #14 is not allowed as a wire size.

NYC is its own animal. They don't play well with others.

I ultimately made an excel sheet and set the distance in increments of 25ft depending how a circuit was from a panel. If nothing else, I will have the excel sheet for future projects.

 

[gene6]

The difference being that I have never been asked by the NYC Dept of Buildings to provide a voltage drop calculation,

We never were either until they did, after conduit was installed, concrete poured, wire pulled etc.
The boss man tried that 'you'r never enforced this before' and they have a very quick and standard denial for that.
Fortunately the company I worked for at the time had good insurance that covered it for them, however our insurance sued the EOR's insurance for 'errors and omissions' as our contracts with them clearly said 'all applicable codes' .
This was all circa 2015 when the energy codes were coming out so dept of B must of been like hey lets enforce this voltage drop now.

 

[gadfly56]

We never were either until they did, after conduit was installed, concrete poured, wire pulled etc.
The boss man tried that 'you'r never enforced this before' and they have a very quick and standard denial for that.
Fortunately the company I worked for at the time had good insurance that covered it for them, however our insurance sued the EOR's insurance for 'errors and omissions' as our contracts with them clearly said 'all applicable codes' .
This was all circa 2015 when the energy codes were coming out so dept of B must of been like hey lets enforce this voltage drop now.

I'm surprised you had an issue. Unless you had very unusual runs and configurations I would think it's hard to get to 5% except for maybe motor loads.

 

[Rock86]

With my situation, I don't understand how they can enforce that I need to document the voltage drop during the design phase. The code states "The total voltage drop across the combination of feeders and branch circuits shall not exceed 5%" It does not say I need to prove that.

 

[ron]

With my situation, I don't understand how they can enforce that I need to document the voltage drop during the design phase. The code states "The total voltage drop across the combination of feeders and branch circuits shall not exceed 5%" It does not say I need to prove that.

The code has a requirement and it usually falls to the design(er) to show compliance with the code. For example, I've been recently having to show calculated fault currents on the oneline so the AHJ can see the SCCR of the equipment is compliant.

You don't need to show behind the curtain, but just that it is compliant. So feel free to make a table and list everything as 4.9% and it only becomes a problem if they want to see the details when something doesn't work.

 

[Rock86]

The code has a requirement and it usually falls to the design(er) to show compliance with the code. For example, I've been recently having to show calculated fault currents on the oneline so the AHJ can see the SCCR of the equipment is compliant.

You don't need to show behind the curtain, but just that it is compliant. So feel free to make a table and list everything as 4.9% and it only becomes a problem if they want to see the details when something doesn't work.

I wouldn't push the limits at 4.9% haha. I do take the time perform the calcs.

We do the calcs for the fault current, but we do not use them on a one line. Well not yet any way.