2

I visited a multiple dwelling house today that had two service panels and two meters connected on the same mains entrance. Each dwelling is wired as such:

Bus (common) → Meter → Fused switch → Conduit to dwelling → Breaker panel

The fused switch is connected to the meter via a short length of EMT conduit, providing ground to the switch box. The circuit that leads to the breaker panel is just armored cable (BX) without dedicated ground.

The breaker panel is your typical Square D QO Loadcentre with a 100A main breaker. The fused switch, however, is rated 60A with two 60A fuses in it and a neutral lug. The meter box has markings for 120V/240V 60A. I understand that the purpose of the 60A fuse is to protect the meter and possibly the circuit that feeds the breaker panel.

  1. Is it normal to have a 100A main breaker installed in a panel that is fed from a circuit with a 60A fuse? If not, should the main breaker be replaced with a 60A breaker?

  2. If the breaker panel had a 60A main breaker, would having the fuse be a requirement? i.e. could the switch be replaced with a non-fused, 60A switch?

  3. Is it possible that the circuit leading to the breaker panel is rated for 100A (plus safety margin), but the 60A fuses have been installed only to protect the power meter rated at 60A?

Improve this question
11
  • Where is the neutral-to-ground bond in all this? That's going to be a huge determining factor as to what's going on here, as that determines the precise location of the service disconnecting means in this mess...
    – ThreePhaseEel
    Mar 18, 2018 at 20:00
  • Ok, I had not considered ground at all. The switch is connected to the meter box with EMT conduit, so at least the switch enclosure is grounded. Then, from the switch, there is no ground going to the service panel (3c: b, r, w). In the service panel, there is a ground-neutral bond and I can see two wires connected independently to the ground and the neutral bus (there is continuity between the two due to the bond). The wires are obscured by the protective service-side cover, which I can't remove now.
    – sleblanc
    Mar 18, 2018 at 20:44
  • The contractor(s) who did the work was sloppy, as the wires are all over the place despite the very small amount of circuits, and there is even a branch circuit that is exiting the box from the service side of the panel, going under the protective cover…
    – sleblanc
    Mar 18, 2018 at 20:46
  • Can you figure out what size the service wires are?
    – ThreePhaseEel
    Mar 18, 2018 at 21:01
  • In an old part of town around me there is an area that originally had 60amp meters and each had a 60amp fused disconnect right below the meter. Quite awhile ago I’m told there was a guy that would “sell” 100 amp upgrades where he would install 100 amp modern breaker boxes in place of the fuses on the inside. But he was a slyster that didn’t pull permits and wasn’t able to get the utility to actually upgrade the service. Years later when a main fuse blew they would finally learn they never got a “100 amp upgrade”, but just a new breaker box that said 100 amp.
    – Tyson
    Mar 18, 2018 at 23:35

1 Answer 1

Reset to default
3

#1 is it normal to have a 100A-breakered panel downline of 60A overcurrent protection? Totally legal. But I'd use a 225A panel. One thing many of us here agree on is running out of panel spaces is bad, and panel spaces are cheap. Both better and cheaper to get a 42-space panel today and only ever use 18 spaces, then get a 12-space panel today have to retrofit a 20-space panel tomorrow and a 30-space panel later still when you add an electric car -- that's just dumb. The big panels we prefer come with big 150-225A breakers, and they often come with "bonus breakers" and ground bars included, so the extra cost can be a wash.

#2 Breakers and fuses protect wiring downstream. Without the 60A fuse, the jumper into your house (#6?) would have no overload protection at all, and if the cable became shorted, nothing would interrupt current and it would burn your house down.

#3 If you want to increase service above 60A, talk to your power company Your service capacity will be limited by the lowest of

  • what the power company is willing to provide
  • the ampacity of your service conductors (frop top of service-drop pole to shutoff switch, which size using the service-conductor rules).
  • the ampacity of your feeder from shutoff switch to main panel (using feeder sizing rules).
  • the max ampacity of your meter pan
  • the max ampacity of your shutoff switch.

It's possible to get combination meter pans/main breakers, with the main breaker serving as the shutoff switch and replacing the fuses. The main breaker and the feeder rules decides the wire size downstream of that breaker.

As far as where is the main grounding point located, some sticklers say the grounding point must be the outside fusing/shutoff switch. However that is awkward in your situation, and for ground-siting purposes I am very comfortable disregarding the outside shutoff and putting the grounding hub in the main panel. They're built for that, and shutoff switches are not.

This presumes there is one main panel. If you fork lines to two panels off that outdoor switch/breaker, things get really complicated.

Improve this answer
1
  • Don't forget to mention that if the ground bond is put in the panel, then the shutoff switch needs to be marked as a meter disconnect...
    – ThreePhaseEel
    Mar 19, 2018 at 22:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.