I called out a repair tech, I have a HVAC air handler that after 4 years started tripping the breaker. It has a subpanel on the unit with two 60 amp breakers that appear to be the right size for the unit. The main breaker panel had a double pole 60 amp breaker and the repair tech came out and replaced it with a double pole 100 amp. I asked him if it was safe upping the breaker like that and he said 100%. Upon further review I found the wiring from the main to the sub is "Stabiloy AA-8000 AL Type SE cable XHHW-2 4 AWG 6 AWG" It seems to have a Amp rating of 75 amps. Is it safe and what do I do to fix it if not.
HVAC Electrical Circuit Breaker
1 - 13 of 13 Posts
Joined
·
11,058 Posts
Post a picture of the AHU data plate.
Joined
·
25,110 Posts
I believe you will find that 2-2-2-4 is rated for 100 amps, so I'd call the bluff on the technician. 4-4-4-6 is rated for 75 amps.
Joined
·
7,409 Posts
It ran for 4 years without tripping a breaker.
Upsizing the breaker is not how to troubleshoot. Regardless of the wire size, he should have inspected the unit spec. plate and taken some amperage readings. What he did is equivalent of putting a penny in a fuse holder.
I'll assume this is a heat pump? For a breaker to start tripping after 4 years you may have an issue with one of the resistance heat strips. (toaster)
Upsizing the breaker is not how to troubleshoot. Regardless of the wire size, he should have inspected the unit spec. plate and taken some amperage readings. What he did is equivalent of putting a penny in a fuse holder.
I'll assume this is a heat pump? For a breaker to start tripping after 4 years you may have an issue with one of the resistance heat strips. (toaster)
The only thing I don't get about that is it has 2 60 amp breakers at the air handler unit and it had a 60 at the main. But the breaker at the main is the one that would trip and hum when you turned it back on. Was it just a bad breaker maybe?
Joined
·
7,409 Posts
It's hard to say what the problem is. But the wire size is what determines the breaker size and vice-versa. That combination has to be matched.
There are some circumstances where a breaker can be oversized, a bit, for some loads requiring more startup amperage. Yours probably does not fit that category. You need to look at the spec plate on your air handler to see what is appropriate.
Joined
·
3,257 Posts
The specification tag on the a/c sets the minimum branch circuit ampacity and the maximum breaker size. On the larger units, the breaker size will almost always exceed the ampacity of the branch circuit since there is other protection provided by the unit manufacturer when it submitted to lab testing and obtained approval with the values on the specification tag. Most inspectors know that the tag values are what they should use.
Only once did I have to supply conductors to meet the breaker size. I gave in to expedite the business opening when it became apparent that this small town combination dairy farmer/building trades inspector of all trades wasn't going to yield.
See example below for a typical tag on a small unit, I'll see if I can find one for the larger ones:
.
.
Only once did I have to supply conductors to meet the breaker size. I gave in to expedite the business opening when it became apparent that this small town combination dairy farmer/building trades inspector of all trades wasn't going to yield.
See example below for a typical tag on a small unit, I'll see if I can find one for the larger ones:
.
.
Attachments
Joined
·
817 Posts
In this case.....
It's 90 amps on the 75° column, which is the one you need to use because the lugs on the breakers are rated for that temp.
100 amps is the 90° rating, which is only used for derating purposes due to temperature considerations.
Joined
·
7,409 Posts
Well you are half way there.
You need to show the specs for your model number.
That will tell you what is installed.
But from the snipped you show, 100 amps sure doesn't look like an option.
You need to show the specs for your model number.
That will tell you what is installed.
But from the snipped you show, 100 amps sure doesn't look like an option.
Joined
·
11,058 Posts
On some that I have installed, the 60 amp breakers in the units are not breakers, but switches. The feed from the panel is the OCPD.
1 - 13 of 13 Posts
