Feeder Size

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philly

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Currently I have a #6 480V branch circuit used to feed a welding receptacle. Personel here want a nother receptacle beside this existing one to be able to plug in another piece of equipemnt. The total FLA of both pieces of equipment comes to 79A. The existing #6 circuit is rated for 65A because you have to used the 75deg rating listed in 310.16. I am told that breaker terminals are rated for 75deg so the 75deg rating of wire size must be used.

In this case the 65A is undersized for the combined load of 79A. I was going to put in a new feeder sized correctly for both these loads. Since both the loads are tools they will not be continuous duty and therfore I do not have to take add 125% to combined load.

I am thinking that I can run a #4 good for 85A and protect it with an 80A breaker. Does this sound right?
 
Are you planing on placing over current protection for each piece of equipment?

You could run 4 AWG copper protected by a 90 amp breaker and that could supply a small panel or a pair of fused disconnects at the equipment end.
 
iwire said:
Are you planing on placing over current protection for each piece of equipment?

You could run 4 AWG copper protected by a 90 amp breaker and that could supply a small panel or a pair of fused disconnects at the equipment end.
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I was planning on using one OCPD rated for 80A and using it to power both of the receptacles directly paralleled similar to the way multiple 120V receptacles are wired on one branch circuit. In other words run a #4 circuit hit one receptacle and then daisy chain over to the other. Can it be done this way?

Where are you coming up with 90A?

Am I right about the 75deg rating?
 
philly said:
I was planning on using one OCPD rated for 80A and using it to power both of the receptacles directly paralleled similar to the way multiple 120V receptacles are wired on one branch circuit. In other words run a #4 circuit hit one receptacle and then daisy chain over to the other. Can it be done this way?
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I don't believe you can do this without a panel.
 
philly said:
I was planning on using one OCPD rated for 80A and using it to power both of the receptacles directly paralleled similar to the way multiple 120V receptacles are wired on one branch circuit.
Click to expand...

What are the rating of the receptacles?

What are the types and ratings of the equipment.
 
iwire said:
What are the rating of the receptacles?

What are the types and ratings of the equipment.
Click to expand...

I believe the ratings of the receptacles are 60A.

The type of equipment are a welder and plasma cutter which will be used as tools possibly both at the same time. I'm not sure what each is individually rated for but the electrican told me the combination of the two is 79A. If I recall I believe one is 44 and the other is 35A.
 
philly said:
I believe the ratings of the receptacles are 60A.

The type of equipment are a welder and plasma cutter which will be used as tools possibly both at the same time. I'm not sure what each is individually rated for but the electrican told me the combination of the two is 79A. If I recall I believe one is 44 and the other is 35A.
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If the receptacles are rated at 60 amps then the circuit ampacity can't be larger than 60 amps.

There is an exception for arc welders.

Take a look at 210.21(B)(3)

Chris
 
raider1 said:
If the receptacles are rated at 60 amps then the circuit ampacity can't be larger than 60 amps.

Chris
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Ok. I guess this is why Iwire recommended using fused disconnects, in order to protect the actual rating of the receptacles. I'm assuing equipment is internally protected.

Dennis Alwon said:
#4 copper is good for 85 amps at 75C. As long as the calculated load is 85 amps or less then you may upsize to a 90 amp breaker. art. 240.4(D)
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I have the 2005 NEC but I think your referring to the article that lets you select the next size breaker up.
 
Ok. I guess this is why Iwire recommended using fused disconnects, in order to protect the actual rating of the receptacles. I'm assuing equipment is internally protected.
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I would like to reiterate that there is an exception to 210.21(B)(3) that allows receptacles for more than one arc welders to be smaller than the branch circuit rating.

Chris
 
raider1 said:
Also you might want to take a look at Article 630.

Chris
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Article 630.12(B) states: Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity.

Does this mean if the branch ciruict was connected directly to the welders I could use an OCPD that was 2 times the the circuit ampacity? I guess the circuit ampacity would still need to be rated according to the load based on 630.11(B), its just the OCPD that can be upsized? Can the plasma cutter be considered as an Arc Welder, or what would it be considered?

Sounds like in my case the outlet ratings are the limiting factor.
 
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Upon thinking about this further I am thinking that my best option is since I already have to purchase a new receptacle, I will purchase a 100A receptacle and at the same time replace the exising 60A receptacle with a new 100A receptacle as well. Then I will have two 100A receptacles which will both be rated for use on a #4 branch circuit rated at 85A and protected with a 90A OCPD.

What do you think?
 
I think you should not try to supply both loads from one oversized overcurrent device. I think you should provide individual overcurrent protection for each piece of equipment.

See 210.20(C)

In general you can not just choose to supply a piece of equipment that requires 30 amps with a 60 amp circuit. A lot of equipment is designed in a way that utilizes the circuits overcurrent protection as protection for the equipment as well.

For example take a look at 422.11

What are the ratings of the plasma cutter?
 
iwire said:
I think you should not try to supply both loads from one oversized overcurrent device. I think you should provide individual overcurrent protection for each piece of equipment.

See 210.20(C)

In general you can not just choose to supply a piece of equipment that requires 30 amps with a 60 amp circuit. A lot of equipment is designed in a way that utilizes the circuits overcurrent protection as protection for the equipment as well.

For example take a look at 422.11

What are the ratings of the plasma cutter?
Click to expand...

I found out that the loads are as follows:

Welder = 64A
Plasma Cutter = 15A

I guess I see what you are saying, since a 90A breaker may not adequately protect the plasma cutter. I would most likely have to have a fuesed disconnect on it. However I would not need to have a disconnect on the welder because 630.12(A) allows the OCPD to be 200% of the welder rating.
 
philly said:
I found out that the loads are as follows:

Welder = 64A
Plasma Cutter = 15A
Click to expand...
With this info, I'd see if the existing conduit can handle the addition of two #12's.

I'd run a new circuit for the new circuit and leave the existing circuit as is.
 
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