Feeder taps and voltage drop

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831

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South Jordan, Utah
Ok...

I've got several sump pumps to feed. I'm going to run a 2/0 to cover voltage drop. If it weren't for the distance, I'd be fine w/ #8. 430.28(3) implies that my tap conductor needs to be not less than the feeder size.

Since the feeder is sized for drop only, should my tap be sized the same?

I am over 25' from the tap point to the disconect @ the motor. A simple sketch:

Sumps7-17-07.jpg
 
You need to provide more information.
Voltage, Motor size and FLA, Type of cable, distance, etc.

Generally speaking, (IMO), As long as the conductors are sized for their respective loads and have upstream overcurrent protection to limit the current on the smallest conductors in the circuit (to their maximum amperage), the tap rules don't apply.

It sounds like you are up-sizing the feeders to reduce voltage drop and protecting the final span to the motor at the feeder supply....If that's the case, you should be OK.
 
hillbilly said:
You need to provide more information.
Click to expand...

Voltage: 208/3
Motor size: 1-1/2HP
FLA: 5.2 (according to my SqD slider)
Type of cable: not determined yet
Distance: avg 1000'

It sounds like you are... ...and protecting the final span to the motor at the feeder supply....If that's the case, you should be OK.
Click to expand...
The tap on the pole (final span) doesn't have fuses/OCP. The OCP will be on the surface near the well casing.
 
831 said:
The tap on the pole (final span) doesn't have fuses/OCP. The OCP will be on the surface near the well casing.
Click to expand...

You need to re-read 430.28

In my opinion...If your tap (if it is a tap) is more than 25' long, you can't use the tap rules.....your final conductors will have to be the same size as the feeder conductors.
If 25' or less, the tap conductors need to be rated at (minimum) 1/3 the ampacity of the feeder conductors and protected at their termination (end) by a overcurrent device that's sized for the tap conductors maximum rated current.

If you're simply up-sizing the feeder to 2/0 cu to reduce voltage drop (this is what it sounds like to me), and protecting the entire circuit from MCC to motor disconnect at the ampacity of #8 cu, (IMO) it is not a tap, and 430.28 does not apply.

Will all of the motors start at the same time?
If so, In my opinion, you have a problem with your design.

steve
 
In my opinion...If your tap (if it is a tap) is more than 25' long, you can't use the tap rules.....your final conductors will have to be the same size as the feeder conductors.
Click to expand...
If it's not a tap, then what is it??? They are taps off of a feeder that has been upsized for VD.

If 25' or less, the tap conductors need to be rated at (minimum) 1/3 the ampacity of the feeder conductors and protected at their termination (end) by a overcurrent device that's sized for the tap conductors maximum rated current.
Click to expand...
The distances is in excess of 25'.

If you're simply up-sizing the feeder to 2/0 cu to reduce voltage drop (this is what it sounds like to me), and protecting the entire circuit from MCC to motor disconnect at the ampacity of #8 cu, (IMO) it is not a tap, and 430.28 does not apply.
Click to expand...
Again, there are several motors (pumps) out there. I'm sending (1) feeder and tapping it @ each motor.

Will all of the motors start at the same time?
If so, In my opinion, you have a problem with your design.
Click to expand...
Let's put it this way, even though it's unlikely, there's nothing that would keep them from starting @ the same time - they're sumps picking up groundwater. I've followed 430.24 in sizing the feeder. Where do you see a problem???
 
Two issues - running current and starting current.

#1 - The conductors (#2/0 AWG) are sized up to handle voltage drop, and normally they would need to be #8 AWG for current, then size the "tap" conductors based on the #8 AWG. in this case you are using # 8AWG and should be fine.

#2 - Hillbilly has a valid point that there could be a problem. The problem occurs in that if all, or even a certain number of motors start at one time, the motors out on the end may not have enough voltage to support starting. This is a very real probelm with larger sized motors, 1.5 Hp, it is unlikely but worth a check. Start by running a motor starting analysis will all the motors running closest to the source, and start the last one. If it starts ok, then also check all starting at one time.
 
The problem as I see it is.....

If you are sending one feeder out to power seven motors (more or less), then your overcurrent protection for the feeder may have to be larger than the capacity of the #8 tap conductors, or else the overcurrent current protection for the feeder may not be able to start all the motors at the same time without tripping.

When you increase the amperage of the breaker (or fuses) protecting the feeder to more than the ampacity of the #8 conductors, you place yourself in the position of having to use the tap rules in regards to the #8 final span (tap) conductors.

If the #8 tap conductors are longer than 25', they won't be legal (code wise).

...But...

If you can protect the feeder with overload protection that is not greater than the ampacity of the #8 final conductors and still have capacity to start all of the motors at the same time, you don't have a problem.

In this case, the #8 conductors will not be considered taps.

It could be a big problem if you install it this way and discover that the feeder overload protection can't start all of the motors without being oversized....i.e....being larger than the ampacity of the #8 conductors.

If that happens, you will have a system that you can't make code compliant without major re-work.

What do you plan to use for overload protection for the #2/0 feeder?
What is the Ampacity of this overload?

Hope that this helps and is clear.

steve
 
Kingpb -

"#1 - The conductors (#2/0 AWG) are sized up to handle voltage drop, and normally they would need to be #8 AWG for current, then size the "tap" conductors based on the #8 AWG. in this case you are using # 8AWG and should be fine."

Logically this makes sense to me. Why should you be required to also upsize your tap beyond the No. 8. However, where in the NEC does it state that? I read no exception in

430.28 (3) "Have an ampacity not less than the feeder conductors"

The way I read it the taps, since they are over 25 ft and not in a high bay, shall have an ampacity not less than the feeders.

I would imagine that requiring 2/0 taps in this situation where an OCPD rating might be 15 amps was not the intent of 430.28 and the Code writers, however I don't see a way around it.

Regards,
 
I don't know the site, but how about putting the transformer closer to the first pump. No upsizing for vd / tap issues.
 
Let's assume the OCP is 40A (OP said #8's are OK normally)

There is no tap here!

A tap is based on the original OCP, not just because you are splicing to a larger conductor...

See "definition" of tap (240.2)
 
I think the definition of what a tap conductor is should help resolve the issue.

240.2 - Definitions. Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

If you have OCP sized for #8AWG, but run #2/0AWG, then by definition it is not a tap conductor, and therefore the tap rules don't even apply.

An alternative is to get clarification from the inspector, prior to bidding and installation.
 
King,

You're absolutely correct. The 2/0 from the OCPD to the first pole (in the OP drawing) is not a tap. Never thought it was, nor does the OP I believe. His concern is at the poles. He wants to tap the 2/0 and drop down to a pump. I believe his 2/0 continues to the next pole, where, I believe he wants to again tap the 2/0 and drop down to the second pump. And so on and so forth right down the line. BTW, I would appreciate it if the OP can verify this. The way I read the NEC given this case, the drop from the pole (2/0) to the Pump has to be 2/0 even though it is a 1-1/2 HP 208V motor.

The NEC doesn't mention the OCPD it says "conductors".

I should add that for instance the motor may have a 15 amp OCPD. recall the OP saying 5+ amps.

Regards,
 
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Let me try to explain again my exact concern about the OP's design.

Since the OP didn't answer my question about the conductor types, I will assume 60C insulation....40A on #8cu.

I'm assuming the Thermal Overload for the motors is in the MCC.

Since the OP can't (by code) use the tap rules, this will require a 40A circuit breaker (or fuses) to protect the #2/0 feeder.
I also questioned what he planned, but didn't receive a response.

My question.....Will the (208V) 40A breaker (or fuses) protecting the feeder start (7) 1 1/2 HP motors simultaneously?

If it will, there is no problem with his design.

If it won't, he has a serious problem, because he won't be able to make it code compliant without major rework....ie....increasing the overload protection of the feeder and the size of the #8 conductors on all of the final spans.
This is because he can't use the tap rules........the final span (taps) would be over 25' long.

I may be concerned about nothing.
Will a 40A breaker start (7) 1 1/2HP 208V motors simultaneously?
It seems like a lot to me.

Just a opinion
steve
 
spsnyder said:
King,

You're absolutely correct. The 2/0 from the OCPD to the first pole (in the OP drawing) is not a tap. Never thought it was, nor does the OP I believe. His concern is at the poles. He wants to tap the 2/0 and drop down to a pump. I believe his 2/0 continues to the next pole, where, I believe he wants to
Regards,
Click to expand...

There is no tap ANYWHERE when going from 8 to 2/0 to 8
 
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