DIY Home Improvement Forum banner
1 - 20 of 31 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
I have two A/C units outside, each wired to a sub panel, with two 30 amp breakers. One breaker per A/C unit. The sub panel is then wired to my main breaker panel on a 60 amp breaker. Is this correct? When my home was inspected, the inspector said something about this being incorrect, but I can't remember what he said I should do. Thank you.

658422
 

·
Super Moderator
Joined
·
9,392 Posts
What did he say was the issue?
Are the breakers within sight of the units and can they be locked off?

No issues that I can see.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #3 ·
What did he say was the issue?
Are the breakers within sight of the units and can they be locked off?

No issues that I can see.
The breakers are with in sight of the units and can be locked off. I think the issue was that it shouldn't be a 60 amp breaker, that it should be a smaller breaker at the main breaker box.
 

·
Registered
Building my last home
Joined
·
909 Posts
The 60 amp breaker protects the wire between the two panels. Did you use #4 copper or #2 AL for the wiring between the panels?

You really need to know the starting current of the two units. Will the 60 be enough to start both units at the same time? It is possible for that to happen.

Are the 30 amp breakers the ONLY disconnecting means for the compressors? If so you need HVAR breakers
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #5 ·
The 60 amp breaker protects the wire between the two panels. Did you use #4 copper or #2 AL for the wiring between the panels?

You really need to know the starting current of the two units. Will the 60 be enough to start both units at the same time? It is possible for that to happen.

Are the 30 amp breakers the ONLY disconnecting means for the compressors? If so you need HVAR breakers
I am not sure about the wires. I will have to check. The 30 amp breakers and the 60 amp breaker allow for disconnecting.
 

·
Registered
Building my last home
Joined
·
909 Posts
Please reread
Are the 30 amp breakers the ONLY disconnecting means for the compressors? If so you need HVAR breakers. Newer condensers may say max fuse or HVAR breaker. I think those are the letters. The CB must be of that style.
 

·
A "Handy Husband"
Joined
·
13,108 Posts
HACR breakers

HACR refers to heating, air conditioning and refrigeration circuit breakers (HACR) . The National Electrical Code permits the use of inverse-time circuit breakers (thermal magnetic) to protect multi-motor and combination load installations that are part of heating, air conditioning, and refrigeration equipment.
 

·
Registered
Joined
·
3,434 Posts
When my home was inspected, the inspector said something about this being incorrect, but I can't remember what he said I should do.
Well, home inspectors are generalists who don't know every bit of Code.
That said, you should look at what is actually on the report, rather than leaving us to guess.

I realize your relationship with the inspector was following him around and listening, but that isn't worth the paper it's printed on. The report is what matters.

The breakers are with in sight of the units and can be locked off. I think the issue was that it shouldn't be a 60 amp breaker, that it should be a smaller breaker at the main breaker box.
Being in sight and within 50' of the units negates the requirement to lock them off.

If he is saying something about breaker size, that may be due to the size of the wire.

#8 copper NM or UF cable is only good for 40A.
#8 copper anything-else cable is only good for 50A.
#8 aluminum, forget it.

#6 copper NM or UF cable is only good for 55A.
#6 anything else is good for 65A.
#6 aluminum is good for 55A.

#4 anything is good enough.

So... if your wire is good for less than 60A, it's not the end of the world -- but you will need to do a load calculation to see if the air conditioner units can fit inside that ampacity. The fact that the A/C breakers are 30A does not need that the 2 units need 60A. Some of that 30A is for design margin to reduce nuisance trips. That's why a load calculation is needed to see if these loads will fit on the wire you have.

So rule 1: Wire >= load.


-----

As far as breakers... once the above is ascertained, and you are sure the wire is large enough for the load, you need to choose a breaker to fit the wire. Same rule here, Breaker <= Wire, except with an asterisk: if the particular breaker size isn't offered, you can round up to the next available breaker.

So rule 2: Breaker <= wire EXCEPT rounding UP allowed.

Example: Your load calculation for both units works out to 51A. 55A wire is acceptable since 51<55. You can round up to 60A breaker because 55A breakers are not offered.

Example: Your load calculation comes out to 58A. 55A wire is not big enough period fullstop. No rounding up allowed. Wire must be replaced.

Example: Your load calculation comes out to 39A. You already have #6Cu UF (55A). You are allowed to breaker at 55A since the wire is good for that. Therefore you are allowed to round up to 60A breaker since 55A is not made.
 

·
Registered
Joined
·
9,300 Posts
#6 copper NM or UF cable is only good for 55A.
#6 anything else is good for 65A.
#6 aluminum is good for 55A.
How does this work—doesn't aluminum fall in the "anything else" category? So doesn't that make aluminum also good for 65A?
 

·
Registered
Joined
·
3,434 Posts
Yeah, typo... or really anything other than NM, UF (or TW if you want to talk about obsolete cable types). All other types are good for 75C or better, which means 75C because of other reasons you can't go 90C.

Nobody makes NM, UF or TW in aluminum, therefore all Al wire counts as 75C.
 

·
Registered
Joined
·
261 Posts
If unit #1 is off for any reason and unit #2 remains running, then unit #2 is on a 60 am breaker - which is illegal, because unit #2 would be on fire at 60 amps.

You may remove the 60 amp and install the two 30 amp in the main panel. Or: you may tied both 30 amp as a single throw in the sub-panel (using the proper bar bought for the purpose).
 

·
Registered
Joined
·
261 Posts
i didn't check your ground wire type or AWG. i assume if the inspector told you that you'd have rememberd it was all about the wire type
 

·
Super Moderator
Joined
·
14,962 Posts
If unit #1 is off for any reason and unit #2 remains running, then unit #2 is on a 60 am breaker - which is illegal, because unit #2 would be on fire at 60 amps.

You may remove the 60 amp and install the two 30 amp in the main panel. Or: you may tied both 30 amp as a single throw in the sub-panel (using the proper bar bought for the purpose).
If one unit is off the other does not get or pull 60 amps. The OP posted a panel with 2 breakers, one for each unit.
 

·
Registered
Joined
·
261 Posts
you omitted if a metal pipe connected the two boxes or not (which could effect grounding and "objectionable current flow on ground", which can be measured on the ground with an amp meter)

there are many manuals on subpanel attachment some specs depend on your power company NEC setup - so I also haven't said I "agree" there is no objectionable current flow. I'd likely measure it, myself, rather than trusting rules found on the internet "would always work".

btw - just call the inspector - no need to figure it out yourself ?! the longer you wait the more chance there is he/she forgets.
 

·
Registered
Joined
·
261 Posts
i hate to add another waiver - but AC are often 240V and your diagram doesn't show 120 or 240, for 240v wiring is different in the panels. i waive that this is an issue - since that's not on the diagram i assume that's all straight - that unit #1 and unit #2 are both getting 240v properly connected / phased.
 

·
Super Moderator
Joined
·
14,962 Posts
i hate to add another waiver - but AC are often 240V and your diagram doesn't show 120 or 240, for 240v wiring is different in the panels. i waive that this is an issue - since that's not on the diagram i assume that's all straight - that unit #1 and unit #2 are both getting 240v properly connected / phased.
The Op shows a 2 pole breaker with a black and a red conductor attached. Why are you trying to confuse the subject?

there are many manuals on subpanel attachment some specs depend on your power company NEC setup - so I also haven't said I "agree" there is no objectionable current flow. I'd likely measure it, myself, rather than trusting rules found on the internet "would always work".
The power company does not follow the NEC. What the heck are you trying to say? Why do you think a manual is needed to secure a few screws through a panel?
 

·
Registered
Joined
·
261 Posts
If one unit is off the other does not get or pull 60 amps. The OP posted a panel with 2 breakers, one for each unit.

WRONG.

I repeat and underline: if unit #1 is not running and unit #2 is running, then unit #2 is effectively alone on a 60 amp breaker

PERIOD
 

·
Registered
Joined
·
261 Posts
WRONG.

I repeat and underline: if unit #1 is not running and unit #2 is running, then unit #2 is effectively alone on a 60 amp breaker

PERIOD
let me be painfully_ clear. If there was a short in the 30A rated unit #2 device the 60AMP breaker WOULD NOT THROW until 60A. With 60A unit#2 , fire rated for only 30A , it would crack in half and set the house on fire before the breaker threw.
 
1 - 20 of 31 Posts
Top