Voltage Drop

[Elect117]

No need to worry about the 75° C. Almost no equipment has 60° C terminations therefore the #6 tap conductor is good for 65 amps. You're correct that the 10' tap rule would apply to the #6's.

While true, the plans should it when the calculation makes the assumption that only 75°C rated equipment, wires, terminations, etc. will be purchased and installed.

 

[ramsy]

Ok so take 227A +50A for the other panel. That's 277A. The run to the trough is 300'.

Engineer has note that VD is to be no more than 2%. So the 2 sets of 1/0 WILL NOT WORK.

I would need two sets of 300MCM. Unreal

1/0 is an efficiency sweet spot, commonly specified for parallel sets.

Your RFI should suggest 4 sets of 1/0, which works w/ Southwire VD @ 2.13%
277A, 208v 3-Phase, 300ft PVC

 

[Alwayslearningelec]

They are telling me I must provide code compliant system which may put me on the hook instead of engineer

 

[infinity]

They are telling me I must provide code compliant system which may put me on the hook instead of engineer

There is no NEC requirement for voltage drop compensation so there is no code issue. NYC might have a VD requirement if applicable.

 

[Alwayslearningelec]

There is no NEC requirement for voltage drop compensation so there is no code issue. NYC might have a VD requirement if applicable.

Yes but other things that were mentioned like the egc size and possibly other not to code issues id be responsible for. I guess.

 

[infinity]

Yes but other things that were mentioned like the egc size and possibly other not to code issues id be responsible for. I guess.

The EC is responsible for a code compliant job. I've never heard of an EC reviewing all of the engineering and every calculation on a bid drawing. The estimator's bid is based on what the designer put down on paper because the estimator is typically not an engineer. If it later turns out that the bid drawing is incorrect then the EC is entitled to an extra to correct the issue.

 

[Dsg319]

I must not understand the set up clearly but how is it compliant to tap one set of paralleled conductors?


Or have I always misunderstood this and it is complaint to tap one single set of parallel conductors?

2020 Code Language:

300.3(B)(1) Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.10(G). The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with 250.122. Connections, taps, or extensions made from paralleled conductors shall connect to all conductors of the paralleled set, grounded and ungrounded, as applicable. Parallel runs in cable traysshall comply with 392.20(C).

 

[ptonsparky]

I don’t see where they are tapping one set. Once you’re past the point of them being parallel, it‘s a tap.

 

[electrofelon]

Explain further. You mean 50-66% of which number?

Of the NEC load calc. Obviously that's a rough rule of thumb and I may tweak it based on what the loads actually are.

 

[Alwayslearningelec]

Of the NEC load calc. Obviously that's a rough rule of thumb and I may tweak it based on what the loads actually are.

Thanks. So if one were to use say 60-70% of calculated load to determine voltage drop that would NOT necessarily be wrong?

I only ask because then I can put it on the engineer saying I as the estimator can't really determine true voltage drop.ad there might and could be different calculations/parameters for determining current at the end of the circuit.

 

[ptonsparky]

Thanks. So if one were to use say 60-70% of calculated load to determine voltage drop that would NOT necessarily be wrong?

I only ask because then I can put it on the engineer saying I as the estimator can't really determine true voltage drop.ad there might and could be different calculations/parameters for determining current at the end of the circuit.

You will both be trying to use CYA language.
Sounds fun.

 

[electrofelon]

Thanks. So if one were to use say 60-70% of calculated load to determine voltage drop that would NOT necessarily be wrong?

I only ask because then I can put it on the engineer saying I as the estimator can't really determine true voltage drop.ad there might and could be different calculations/parameters for determining current at the end of the circuit.

IMO it would not be wrong at all, in fact it would be GOOD engineering. OF course there is a potential for an argument with one side thinking it is "obvious" that one should use the load calc value, ya never know. Where does it put you at with wire size if you use say 66%? Sometimes part of it is also playing around with values and seeing what conduit and conductor sizes are needed for different values, and using that to guide the decision. Another strategy is go higher with 80% as that figure matches the continuous load and largest motor fudge factor.

 

[Elect117]

I agree with everyone's opinion. You can't estimate a job that has been "engineered" incorrectly. It is one thing if something arises during construction but estimating a plan set that is wrong is like a cascading set of issues.

Do the plans go through city plan check review prior to estimation? The plan checker might flag the issues for you.

 

[MyCleveland]

Thanks. So if one were to use say 60-70% of calculated load to determine voltage drop that would NOT necessarily be wrong?

I only ask because then I can put it on the engineer saying I as the estimator can't really determine true voltage drop.ad there might and could be different calculations/parameters for determining current at the end of the circuit.

You are down a rabbit hole again trying come up with a conscientious solution for a failure of the plan author.

Post #46 by "infinity", tells you everything you need to know.
If the GC tells you need to follow the "PLANS"...then just pick a percentage and disclose it in your bid.
Make sure to indicate the EE must update plans to reflect this new feeder size and resubmit before construction phase because any sharp EI is going to see you installed something different than original plans.

Make EVERY effort to indicate plans are incomplete and you should not be forced to correct deficiencies unless the EE wants to help on bidding, procuring material, juggling manpower, assist in fighting other trades, walking the job multiple times with different EI's, etc....

 

[kwired]

Since voltage drop is not an NEC requirement, I don't see that any justification is needed for whatever method or diversity Factor is used.

The issue becomes what is the amount of VD to be based on? Full designed load conditions, voltage during motor starting or other short term starting surges of current?

You can have the conductor ability to hold at a certain level but the source impedance could still cause significant drop in some those short term surges of current. Which isn't always a bad thing.

 

[gene6]

There is no NEC requirement for voltage drop compensation so there is no code issue. NYC might have a VD requirement if applicable.

FYI the energy code is all of NY state, and covers VD.
And its 5% total not 2%,
In the NYC electrical code there is another VD requirement, also they ban 14 AWG.
The energy code also covers lighting, motor and transformer efficiency all things that should be in plans that comply with the applicable code.
I have a plan set here with 3 pages on just the lighting part of the energy code.