Replace old subpanel or not?

11 years ago

Friend had old main panel with 100amps and no spare spaces. Getting everything upgraded - new main panel with 200amps already done last month.

House is 100 years old with mixed knob& tube wiring and new NM romex wiring in parts that were remodeled. For example the kitchen was remodeled 4 years ago and since it was right above the service room in the basement, they ran all new wiring to the panel.

Currently, remodeling entire 3rd floor and contractor is putting a 16 space sub-panel on the 3rd floor to connect all the lights and breakers for the entire 3rd floor to include 2 bathrooms on 3rd.

In the Kitchen on the 2nd floor is a very old Square D QO 125 amp sub-panel with 8 breakers - I think it's fed from a 60amp breaker from main panel, but I don't remember size.

All of the wiring coming into this old subpanel is old knob and tube type. None of it is for the kitchen. Some of the breakers power the other old rooms on the 2nd floor which have old plaster covered walls. Some of it originally also powered the 3rd floor but is no longer needed, so on the 3rd floor the contractor cut the old K&T lines and put junction boxes wherever he cut the knob& tube wire since it is still live due to possibly going to other locations on the 2nd floor and basement and the Attic room on the roof. The entire 3rd floor was newly wired with NM (romex).

Back to the old 8 space subpanel in the kitchen. It is old - and it is working fine. Should it be replaced with a new one? They would simply be swapping out the old box with a new one and not adding any arc fault switches since it is all knob and tube wiring and has shared neutrals. Or should they just leave the existing old panel as is.

Cost is not an issue here since the panel is less than $50.
They will not be changing any of the knob and tube wiring feeding it since it goes to areas on the 2nd floor that were not remodeled at all so that will all stay.

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Comments (10)

glennsparky
11 years ago
Square D QO is still in production and well respected. The breakers are current and modern. Only replace the box if there are safety issues such as visible corrosion, burn or arc marks, or pitting or arcing where the breakers contact the power bus. You could probably get arc fault breakers to fit this existing box. They would be safer, but expensive. And nuisance tripping may drive you crazy. Or you could look at it this way. If an arc fault keeps tripping maybe that circuit needs to be replaced.
glennsparky
11 years ago
If by "shared neutrals" you mean MultiWire Branch Circuits, some companies do make double pole arc faults for MWBCs. I don't know if square d makes them though.
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The few things I'd be using that aren't universal anyway are mostly marked 50/60 hz, when I moved from Canada to NZ then Australia back in the 70's we had some issues with a couple of electric motors, but most were fine. I realise there's technically no 'neutral' in NA 240, but I'm pretty sure it would be fine. My Dad brought a Sears 240v Radial arm saw from Canada back to NZ, he said when it was new the onboard breaker tripped a bit (maybe back in the 70s it was rated 220v?) but when it got a bit older it was fine. As for phase, I'm not sure what you mean. It's all single phase, just like here in Canada. My plan would be to either use a 240v plug like we have here, or I could add an Australian one (I kept a few outlets) which I suppose technically might not be kosher since it won't have the CSA rating but they are, nevertheless, rated 250v or higher. It is an different system there, they generally don't use junction boxes there (unless they're surface mount, or there's an inline join) because, for one, outside walls didn't used to be insulated, also, instead of wire nuts, they use an insulated brass joiner with a grubscrew. I kind of liked that system, harder to mess up and perhaps a little more reliable, but slower to fit I suppose.
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kzaker you need to post a NEW thread, rather than asking your question in the middle of someone else's. I don't immediately recall how it works out but I have encountered many services, including recently-installed-and-apparently-approved ones, consisting of a mobile-home-style "meter main" or CSED (meter socket and main circuit breaker in one box) feeding regular old SE cable (NOT SER). ie, 3-wire. Given how many of these my local power company has apparently approved, I am inclined to believe this is legal in some certain scenario. Further, the apartment complex I grew up in, consisting of four buildings of six units each, which is wired very well (other than having FPE breakers - which weren't perceived as a problem back then) is also wired the way the original poster describes. Power comes in to a little shed on the end of the building, which contains six meter sockets with built-in 100A circuit breakers. 3-wire cables leave these sockets and go to the apartments' individual breaker boxes, which are wired as MAIN panels. I'm moving a service within the next couple weeks. The power company guy came out and looked at where I want to put the meter, and approved it. As part of our conversation, he stated that if I put the panel where I originally wanted it, I will need an outdoor disconnect due to distance (2 feet??!!). Supposedly I can still use SE, however. When is a panel fed from an outside disconnect considered to be a subpanel? Unless I'm surrounded by illegal services, it sometimes isn't. What's the distinction? I think the original poster's existing wiring is probably correct.
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Thank you very much for your answer. I truly appreciate you. I believe I could also upgrade to a 90amp and still keep the 4 gauge leg. It would save quite a bit of money, and I believe it would be sufficient since I only added a 30 amp. I found some 4 gauge couplers that 'look' good. https://www.walmart.com/ip/Polaris-It-Series-Insulated-Connector-4-14-Awg/110335012?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227069117749&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=176607737218&wl4=pla-282596616956&wl5=9027823&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=110335012&wl13=&veh=sem#about-item Do you think that would work?
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Ron Natalie
11 years ago
Square D does NOT make any 2 pole arc faults. They're not that common even in other lines. CH does not make them any more. GE does.
Ron Natalie
11 years ago
Note, that it is unlikely that there are any MWBC with k&T. If you have any "sharing" of neutrals it most likely is NOT going to be solved by a two pole AFCI.
kisu
Original Author
11 years ago
Yes - it is all old style K&T going to this subpanel so no way to add Arc Faults. Box looks clean and since it is in an interior kitchen wall it does not appear bad from a quick look. It's maybe about 65 years old.
brickeyee
11 years ago
Even touching K&T can cause prob\lems.

Some of the wire is rubber insulated directly over bare copper (lead plating the copper was added later to protect the rubber).

The rubber and copper react to make the rubber insulation extremely brittle.
The slightest flexing (even vibration) often results in the insulation falling away in large pieces.
Ron Natalie
11 years ago
Are you saying there is K&T as the FEEDER of the subpanel? HOLD THE PHONE. This is a different story. Something is very wrong here. Replace that feeder.
kisu
Original Author
11 years ago
no no no - sorry for the bad explanation. The feeder wires coming from below this subpanel and going straight to the main service are not K& T. They appear to be about 6AWG-
definitely fatter than 8awg - I'll have to look again. The main service panel has a 40A breaker to this sub-panel. And yes sometimes they had issues if a vacuum is plugged in and couple other things.

But now that the entire 3rd floor is being taken off the load of this subpanel, I am thinking they won't have an issue anymore when construction is done.

You have convinced me that the old subpanel in the Kitchen should just stay or they risk cracking the old K&T lines coming into it when doing a swap to a new model panel.

But should we keep the 40A breaker in the main service? If they continue to have problems when plugging a vacuum on the 2nd floor (where most of the plugs are still 2-prong and fed by K&T lines) - should we change it to a 50A breaker?

Thanks
Ron Natalie
11 years ago
You can size the breaker for the feeder to the largest that is applicable to the remote panel and the feeder conductors themselves. If you've really got #6 going there you could up the feeder breaker to 60A provided the subpanel can handle it.
Ron Natalie
11 years ago
...which would be unlikely that it wasn't.

One thing I'd be sure to check on some ancient K&T based panel is whether that subpanel is properly wired as a sub panel. Normally things things were left over main panels repurposed as subs when wiring got updated. Now if the only thing coming off that panel is K&T, there's not really an issue (K&T doesn't usually have equipment grounds). However if someone hacked in a piece of NM or something with a ground, you better make sure that ground is *NOT* just tied to the neutral conductor.

Replace old subpanel or not?

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Replace old subpanel or not?

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