Amerage question

[Russell J. Hensel]

I have seen several different answers and got different answer from each of the licensed electricians I know. Here is the situation.

Pool sub panel is a 90 amp Cutler Hammer breaker wired with 4 AWG aluminum wiring. The type of wire is THHN2. Now from what I could get from it is that this wire is MAX rated for 75 amps of power. I know the higher temperature rated wiring can facilitate more power. But doesn't the connection point also have to be properly rated.

So is this wire good enough for a 90 amp sub panel fed from the main panel and were can this be found specifically.

Thanks in advance.

[Michael Larson]

What is the protection ahead of the wire?

[Russell J. Hensel]

sorry don't understand the question....coming from a 200 amp cutler hammer main breaker box..

[Michael Larson]

Was the wire to the sub protected at the 200 A panel?

[Russell J. Hensel]

yes, it was

[Michael Larson]

Originally Posted by rhensel

yes, it was

By what size breaker or fuse?

[Jim Port]

Your answer is in Table 310.16. Even using the 90 degree column #4 AL is only good for 75 amps max. Using lower rated columns would reduce this rating.

You are correct that the terminations would also affect the ampacity. AFAIK I have not seen a 90 degree termination.

Ambient temperatures and number of conductors in the raceway would also have an impact.

[Russell J. Hensel]

It was a 90 amp breaker coming from a Cutlet Hammer 200 amp distribution panel that went about 70 feet to a cutlet hammer pool equipment sub panel...

[Russell J. Hensel]

4/O aluminum wiring was the main incoming wires...

[Russell J. Hensel]

Thanks Mr. Port...everywhere I looked I was right, but then a master electrician said I was wrong. This was at a re-inspection and I did not just take his "its OK' for granted. I appreciate your response and help and this is the exact reason why INACHI ROCKS!

[Michael Larson]

I was on the phone but I see Mr. Port helped out.

[George P. Wells, CMI]

Did the electrician explain why he believed the installation to be acceptable? 75A may not be a standard breaker size for that manufacturer. If a 90A breaker is the closest standard size, then generally it would be acceptable to protect the circuit at the next standard breaker size.

Another possibility is that building codes usually allow for variances from the code when calculations are made under the supervision of an engineer. In a situation where you a single motor load on a circuit, the manufacturer of the motor may have made calculations and published installation requirements that do not necessarily meet any local, regional or national code but the local inspectors will allow the installation based on the manufacturers specs.

As an electrical contractor, I had a few occasions where I installed equipment based on manufacturers recommendations. The local inspector would sometimes disallow the installations based on the building codes until I provided copies of the manufacturers installation specs.

Originally Posted by rhensel

Thanks Mr. Port...everywhere I looked I was right, but then a master electrician said I was wrong. This was at a re-inspection and I did not just take his "its OK' for granted.