My question is in the title. Here are the details, I bought a 125 amp sub-panel but I only need 60 amps. The main service panel is 200 amps. I ran a 6/3 awg wire to the sub-panel. Can I install a double pole 60 amp breaker in the main panel to power the sub-panel or do I have to use a double pole 30 amp breaker? Any help would be greatly appreciated.

First up, the cable feeder from the main panel must be a 6-3 w/ground nm romex or SER cable. The 125A subpanel can have a 60A double pole breaker for the 120/240vac disconnect. Connect the two ungrounded hot wires to their respective bus terminals. A 60A two pole breaker will be at the main panel also.
Secondly, the neutral White insulated wire must connect to the grounded terminal bus that will be isolated from the box shell enclosure.
Third, the bare conductor must be connected to the Equipment Ground Conductor (EGC)bus Terminal. IMPORTANT: If there is a green screw in the neutral bus terminal it needs to be removed to isolate the Neutral. This is very important.
Note: If this subpanel is in a garage MIL kitchen, that has a metal waterpipe, the pipe must be grounded with a #6 Cu bonding conductor in that panel EGC terminal block.

Sorry but need to offer a couple of corrections.

#6 Nonmetallic cable ,AKA Romex, copper, is not rated 60 amps, only 55 amps, per NEC Setion 334.80, which limits NM cable to the ratings list in the 60 Deg C column of Table 310.16.

SER cable implies aluminum cable, which #6 is only rated for 40 amps.

Therefore, a 60 amp feeder will need to be either AC (BX) cable, or MC cable, or THHN wire pulled in conduit, i.e. EMT,PVC,flexible metal or nometallic conduit.

A subpanel in a garage, not sure what MIL Kitchen means, is not the driving factor to bonding metallic systems. If the metallic water system is city water line which is used as the primary grounding electrode , bonding it to a subpanel is not required.

If the water system is metallic, and well or city utility, that does not fulfill the requirements as a primary grounding electrode, and existed before the subpanel is installed anywhere, the metallic water system, or any metallic piping system, should have been bonded to the grounding of the maiin panel already.

Note, before bonding of any natural gas piping provided by a utility, must always check with that utility to determine if grounding or bonding to their piping is allowed. Using a natural gas line as an electrode is not allowed.

Quote:

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Originally Posted by tkrussell

Sorry but need to offer a couple of corrections.

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Thanks for covering tk. I agree with your observations.

Would using #2 SER Al ( Cu SER is rare) with a 70Amp breaker be more economical in this case? The cost is less than using a copper feeder and the breakers cost is the same as a 60A. Conduit or MC is very expensive and difficult to install in residential stick-frame wiring unless the local authority requires it or this is in Chicago.

This 70Amp suggestion is based on main structure derived installation, 4-wire subpanel with isolated neutral terminal bar and no additional bonding of existing metal pipe.

Please forget any comments about mother-in-law quarters in a garage.

Oh Ok I get it now, MIL. Just did not occur to me what the acronym meant.

Yes absolutely #2 SER is a very good alternative, relatively inexpensive, readily available, and the upside is the feeder can easily be upgraded to a full 100 amp feeder in the future, providing the panel is rated 100 amps, which this one is.

Yes I am aware that Chicago requires everything be installed in conduit. And some people complain about MC. Even still if conduit is required in a certain location, #2 Al XHHW pulled is a reasonable alternative to SER cable.

Ok, here is what I got.

Can that 125 amp panel be use as a 60 amp panel? I've already have a 6/3 AWG with ground wire fed to the sub panel from a 200 amp service panel. I have a double pole 60 amp disconnect breaker at the main panel for the sub panel and the 6/3 wire is not in any protective shield like and EMP. The wire is ran over the ceiling joice. The sub-panel will be powering up a kitchen, 2 bedrooms, a bathroom and a living room. Do you guys see anything wrong with this setup? Is 60 amp in most case sufficient enough to power all that? BWT: this house is in southern California, and thank you guys for responding as lighting fast as you did. = )

Feeding the 125 amp rated panel with 60 amp is fine. 60 Amps may be enough to feed the rooms you mention, as long as they are of normal size with normal appliances and load. can't say for sure without knowing square foot, and what loads will be connected.