#4 AL OCP

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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
200A residential panel in garage for supplying ACCU's, 240V Appliances, pool, and a panel in the house to supply the gas furnace & all the other loads.

The house panel feeder is original #4SE aluminum cable. 310-15(b)ampacity chart lists
#4 AL rating at:
55A@60*C 65A@75*C.
I assume that going up 5A to the next size up OCP applies.

Can this feeder go on a 70A circuit breaker?
Or does the 60* rule apply for residential feeders <100A, forcing me to stay with a 60A CB?
I am not a fan of small aluminum wire but the homeowner doesn't want to replace the feeder.
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
The house panel feeder is #4 SE aluminum as installed when the house was built in 1974. It is on a 2P50A now and the homeowner called today saying it tripped.
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
ptonsparky said:
I agree a 60 is cheap and you need to check the load. Also check the buss and stabs on the breaker. Don't put a new breaker on a buss that is bad.
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New panels and breakers, buss is fine. The question is what meets code re: OCP for the 4AWG Aluminum feeder in this residential application. Does a 60A meet Code? Better yer, a 70A?

I personally despise AL conductors and only use it for Service Entrance conductors -and begrudgingly when I do. I'm an old-school commercial pipe & wire man who only trusts copper... but this isn't my house, and I have to deal with the homeowner.
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
ptonsparky said:
I agree a 60 is cheap and you need to check the load. Also check the buss and stabs on the breaker. Don't put a new breaker on a buss that is bad.
Click to expand...
The question is maximum breaker permitted for this 4AWG SE feeder in this particular application. Lots of nuances in residential codes. And I despise aluminum
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
I want to say a 70A breaker meets code to protect the 4AWG type SE Aluminum feeder (SE is rated at 65A@75*C) but I found a contradictory statement about maximum 60* rating applying to residential wiring circuits of 100A or less. Does this apply, as this appears to be qualified as a residential sub-panel?
A 60A will provide limited reserve and MAY remedy the present 50A tripping problem, but a 70A OCP would be a substantial improvement and probably permanently remedy the problem ONLY IF IT MEETS CODE IN THIS APPLICATION.
 
T

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
GarwoodV6 said:
The house panel feeder is #4 SE aluminum as installed when the house was built in 1974. It is on a 2P50A now and the homeowner called today saying it tripped.
Click to expand...
Yes I agree the question is about an increase in ocpd size.
I would first make sure it is needed before rounding up. The conductor has to carry the load. Rounding up the ocpd with an increased load beyond the rating of the conductors ability to carry the load could be dangerous and lead to a conductor failure.
Should we ask ourselves:
What if the breaker just needs replaced. What if you can get a 55 amp replacement. Just because a breaker trips I would not increase the size because I can. Why did it trip or at least consider why it did.
If has work since 1975 on a 50 amp. What changed.

If the thread was just about ocpd for #4 al@ 75c se cable I would have just read and watched. Once it said breaker trips. I have to ask myself why.
What if the al wire on the breaker and a poor connection and that is why it tripped.
Just throwing out a question to help a fellow electrician out.
Using the round up rule the conductor has to carry the calculated load.
Other than that sorry I chimed in.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
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State Electrical Inspector (Retired)
Addressing your direct question. Assuming the #4 AL SE has 75° conductors and the terminations are rated 75° (both highly likely siktuationsP), the cable can be used at it's 75° ampacity of 65 amps and, if the actual load does not exceed 75 amps, it can be protected by a 70 amp breaker (assuming the panel buss in rated that high)
 
Sberry

Sberry

Senior Member
Location
Brethren, MI
Occupation
farmer electrician
For some reason (I know its not a direct answer) I thought it was limited to 60. As a practical matter,,, I never use it, I use number 2 and have put a whole bucket full of 60's on them and NEVER had a call for a trip including a couple busy garages and one with a fair amount of welding. Never had a loose connection, have at least 9 feeds of my own alum.
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
LarryFine said:
Do you have a load calc?
Click to expand...
No load calc. It was on a 60A before I replaced the Main panel last fall.

Aluminum makes me nervous, and I've seen all sorts of foolish mistakes including oversized breakers in residential panels over the years. I couldn"t find proof that I could safely put it on a 60A in the code book when I installed the panel last fall, and decided to play it safe with a 50A and recommended it be replaced with a larger copper feeder.
Call me paranoid...
 
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Sberry

Sberry

Senior Member
Location
Brethren, MI
Occupation
farmer electrician
I dont think the mistakes are isolated to alum, most are made on copper. Good share of the worlds power is delivered alum at least at some point, in this country from kettle to meter for sure.
 
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GarwoodV6

Member
Location
Houston suburbs
Occupation
30 year commercial Electrician
The customer replaced the house panel with a larger panel with 125A bus 3 years ago during a remodel, re-using the existing #4AL feeder.
 
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