Conduit Fill/ Derating

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A/A Fuel GTX

A/A Fuel GTX

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Electrician
Here is the scenario......

1 1/2 EMT

61 # 12 THHN CCC's per Annex C Table C.1

Derating of CCC's per 310.15 (B) (2) (a) 30 X .35 = 10.5A

Can 20A OCPD's be used as long as the load is within the 10.5A allowed?

Also, I'm a little unclear about counting the grounded conductor as a CCC. In a situation where a common grounded conductor is serving three circuits originating from a three phase panel, would we count the grounded conductor as a CCC? What about a single phase situation with one grounded conductor serving two circuits? What about one circuit with one ungrounded and one grounded conductor? 310.15 (4) is a little hard for me to grasp. :x
 
Can 20A OCPD's be used as long as the load is within the 10.5A allowed?
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No the conductor must be protected at or below its ampacity. The 10.5A is the ampacity of the conductor under those installation conditions.
In a situation where a common grounded conductor is serving three circuits originating from a three phase panel, would we count the grounded conductor as a CCC?
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Only if the majority of the load is nonlinear.
What about a single phase situation with one grounded conductor serving two circuits?
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This grounded conductor is not a current carrying conductor.
What about one circuit with one ungrounded and one grounded conductor?
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This grounded conductor is a current carrying conductor.
Don
 
What are the loads that these circuits are feeding? If your derated values are 10.5 amps the largest OCPD you could use is a 15 amp device. This is only if the circuits are not multi-receptacle circuits. If they are, you'll need to change the installation.

The grounded conductor (neutral) in a three phase, 4 wire circuit is not a CCC if the circuits do not contain more than 50% harmonic current.

The grounded conductor used with two phase conductors in a three phase wye system would count as a CCC. And it would also count in any 2 wire circuit.
 
infinity said:
What are the loads that these circuits are feeding? If your derated values are 10.5 amps the largest OCPD you could use is a 15 amp device. This is only if the circuits are not multi-receptacle circuits. If they are, you'll need to change the installation.
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This installation is in a computer " clean " room. So if I understand your answer correctly, if these loads were one piece of utilization equipment each, I'd be OK but if the circuits were feeding a multi receptacle circuit, it would not be allowed? If so, how would you change the installation to comply?
 
Can 20A OCPD's be used as long as the load is within the 10.5A allowed?
Click to expand...
No the conductor must be protected at or below its ampacity. The 10.5A is the ampacity of the conductor under those installation conditions.


Don, if that were the case, how would I protect the coductors at or below the 10.5A?
 
m73214 said:
infinity said:
What are the loads that these circuits are feeding? If your derated values are 10.5 amps the largest OCPD you could use is a 15 amp device. This is only if the circuits are not multi-receptacle circuits. If they are, you'll need to change the installation.
Click to expand...

This installation is in a computer " clean " room. So if I understand your answer correctly, if these loads were one piece of utilization equipment each, I'd be OK but if the circuits were feeding a multi receptacle circuit, it would not be allowed? If so, how would you change the installation to comply?
Click to expand...


You are allowed to go up to the next standard size OCPD if the load served is not a multi receptacle circuit. But your connected load still can not exceed the derated value of the conductors.

In your installation you would need to install more conduits and split up the circuits to get their derated value within a usable range.
 
Tom,
Don, if that were the case, how would I protect the coductors at or below the 10.5A?
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Ten amp breakers are available. Also infinity is correct, if this is not a multi outlet circuit for cord and plug connected equipment, you could use a 15 amp OCPD on these conductors.
Don
 
It was clarified that the use of a 15-ampere breaker would be permitted as long as the circuit supplied an individual piece of electronic equipment where the load did not exceed the adjusted ampacity of 10.5 amperes. It should be noted that the 15-ampere limitation, while applicable in this instance, would not necessarily apply to motors, welders and some other Code recognized loads. In each case the OCPD could be higher than 15-amperes.
 
It was clarified that the use of a 15-ampere breaker would be permitted as long as the circuit supplied an individual piece of electronic equipment where the load did not exceed the adjusted ampacity of 10.5 amperes.
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As long as the equipment is hard wired or served by a single receptacle and not a duplex, I agree.
Don
 
don_resqcapt19 said:
Tom,
Don, if that were the case, how would I protect the coductors at or below the 10.5A?
Click to expand...
Ten amp breakers are available. Also infinity is correct, if this is not a multi outlet circuit for cord and plug connected equipment, you could use a 15 amp OCPD on these conductors.
Don
Click to expand...

don_resqcapt19 said:
As long as the equipment is hard wired or served by a single receptacle and not a duplex, I agree.
Don
Click to expand...

"Assuming" we have 10.5A on the circuit, protected by a 15A OCPD....what is the recept. rating? 15A?

I'm looking at Table 210.21(B)(3), I keep seeing "...a branch circuit supplying two or more eceptacles..."
Anyone have the right article to show don and infinity's point?
 
celtic said:
don_resqcapt19 said:
Tom,
Don, if that were the case, how would I protect the coductors at or below the 10.5A?
Click to expand...
Ten amp breakers are available. Also infinity is correct, if this is not a multi outlet circuit for cord and plug connected equipment, you could use a 15 amp OCPD on these conductors.
Don
Click to expand...

don_resqcapt19 said:
As long as the equipment is hard wired or served by a single receptacle and not a duplex, I agree.
Don
Click to expand...

"Assuming" we have 10.5A on the circuit, protected by a 15A OCPD....what is the recept. rating? 15A?

I'm looking at Table 210.21(B)(3), I keep seeing "...a branch circuit supplying two or more eceptacles..."
Anyone have the right article to show don and infinity's point?
Click to expand...


Look at 240.4(B).
 
celtic,
"Assuming" we have 10.5A on the circuit, protected by a 15A OCPD....what is the recept. rating? 15A?
Click to expand...
210.21(B)(1) permits a single receptacle to have an ampere rating not less than that of the branch circuit.
Don
 
Another option is upsizing the wire, which probably requires a larger (or multiple) conduit(s), which is why an installation design always starts at the load.
 
LarryFine said:
Another option is upsizing the wire, which probably requires a larger (or multiple) conduit(s), which is why an installation design always starts at the load.
Click to expand...


But Larry, I frequently work with engineers and many of them don't even understand derating and they are doing the design. :twisted: :twisted:
 
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