Old CH Panel & Wiring...Questions

[vtsoundman]

I have a old CH 100A main panel with 16ckts. By in large, everything looks like it was done by a pro...and from what I can tell, followed the codes of the day.

Question 1:

This panel and oven install was done in the early/mid 70's...It has a 30A breaker feeding a 4.6kW nameplate single wall oven with number 12 wire run in EMT/BX conduit using what looks like is THHN copper conductors).

Current NEC table allows 25A on #12 when run in conduit/with rated terminations.

4600W @ 240 = 20A, so a 25A wire size is technically correct.

Current NEC cycles require 20A OCPD for #12...however, was there a time where the NEC allowed a 25A fuse/breaker for #12?

AFAIK, Code has always nearly allowed rounding up for breaker sizes - so the 30A breaker may not be wrong if CH did not offer a 25A at the time of install.

Question #2:

There are two 100A 'long' form CH2100L breakers in the box - the main 100A breaker and a 100A subpanel breaker. Both are showing signs of water/rust and I'd like to replace them both. From what I understand, using a CH2100 (short version) is just fine & a approved use for the 100A sub...I just haven't been able to confirm the same is true for the main breaker.

A CH 100A long breaker (CH2100L) looks like top one here:

I do know the newer style (short form) CH2100 is acceptable to use as the subpanel breaker. Does anyone know if I can use the CH2100 as the main breaker as well? Cost difference is 4x ($250 or more) for a used/recert breaker.

Some of the breakers within the panel are in rough shape (rusty) and I am replacing most of them. The panel busbars are in good shape, so no reason to swap the panel now...Eventually we will upgrade the main service and will use all new equipment, but that is a few years off.

 

[vtsoundman]

Here is the panel with cover removed. The empty space is for the oven breaker. Most of the house is run off the 100A sub panel. There is a 50A sub that runs the workshop...

I confirmed the oven wire is indeed #12 600V, didn't see the wire type...pulling new wire would a bear not a good use since it will eventually be replaced.

Other circuit:
20A MWB feeding bathroom heater, bathroom, and bedroom.
20A MWB feeding pool
50A feeding workshop subpanel
100A feeding main house panel
All other ckts disabled (incl a 30A knob & tube fuse panel that was still live and in use)

 

[vtsoundman]

Well I called Eaton and spoke to one of their knowledgeable techs...He confirmed the use of CH2100 short form for the subpanel feed. He wasn't sure about the main allowing a hold down kit. Any of the old time sparky's know a hold down kit will work?

He also confirmed that CH likely did not offer a 25A dual pole breaker in the early 70's (the 69 catalog did not have it). So the question is: did the NEC of the early 70's allow a #12 wire with a 25A breaker?

 

[vtsoundman]

Well, since I am talking to myself in this thread... I guess I will keep going.

OK:

If my oven were a range...Ranges are not considered a continuous load and per 220.55, we can use the derating factor of service feeders to size the individual branch circuit for the oven. Therefore, a range (with an oven & burners) 4600W I would be able to use 15A breaker and #14 wire.

However, per another footnote with 220.55, a wall mounted oven has to follow a different footnote - and its nameplate shall be the rating of the circuit. No derating or uprating required. Therefore 4600W/240 = 19.16A for a branch circuit rating of 20A.

The proper breaker for the oven would be 20A. I would hazard a guess that the PO of my house simply dropped in a 30A breaker b/c that is what he had at the time.

This is further supported by the manual of a similar GE single wall unit, units up to 4.8kW @ 240 should be on a 20A circuit (#12 w/20A OCPD).
...

Ranges contain ovens...and this chart is pretty interesting.

 

[Norcal]

Well I called Eaton and spoke to one of their knowledgeable techs...He confirmed the use of CH2100 short form for the subpanel feed. He wasn't sure about the main allowing a hold down kit. Any of the old time sparky's know a hold down kit will work?

He also confirmed that CH likely did not offer a 25A dual pole breaker in the early 70's (the 69 catalog did not have it). So the question is: did the NEC of the early 70's allow a #12 wire with a 25A breaker?

The 25 ampere rating is not used for branch circuits, nor is NM cable "Romex®" allowed to use the 75 or 90 degree columns,NM must be sized from the 60 degree column* there are areas where 12 AWG is allowed to be used at 25A, but that oven is not one of them.

* It was about 1985 when NM cable was changed to have 90 degree insulation, but still must be sized from the 60 degree column.

 

[vtsoundman]

The 25 ampere rating is not used for branch circuits, nor is NM cable "Romex®" allowed to use the 75 or 90 degree columns,NM must be sized from the 60 degree column* there are areas where 12 AWG is allowed to be used at 25A, but that oven is not one of them.

* It was about 1985 when NM cable was changed to have 90 degree insulation, but still must be sized from the 60 degree column.

Thx for the response.

The oven wiring is #12 THHN 600v...Temp rating is unknown.

Given that the oven ckt is sized per nameplate, think I should be all set to drop in a 2pole 20 and call it a day?

via pyramid energy waves.