Originally Posted By: Dennis Bozek
This post was automatically imported from our archived forum.
The only way to determine the ampacity of a service is to determine the wire size…PERIOD! Anything else you use will not tell you what the actual ampacity is. If you are unsure what the wire size is and unsure what the size is with either copper or aluminum wire…then you need to have it inspected by a electrician. The rating found on the panel is only the rating for the enclosre and means only that the main feeders can be at the rating of the enclosure or less. The main breaker might be 100 amps but if it is fed with 6 gauge…it is no longer a 100 amp panel. What it is is a 60 amp panel with a oversized main breaker. So regardless of what the enclosure states, what the main breaker states, and what the home owner states…the only physical check any one can make to determine the actual ampacity of the service is the wire size and type of wire.
This can be difficult to do. The most common way to determine wire size is to look for markings on the wire itself. However, to do this it may be necessary to handle the wire inside of the panel and if you are unaware of the hazards that exist in doing this or unfamiliar with what you can safely touch in a panel.....recommend it to be checked per a sparky. If it is SE cable, the jacket on the outside of the cable is typically stamped or marked with what type of wire it is and what size wire it is. This can be done somewhat safely because the SE cable is outside of the panel itself. Another way to determine wire size would be with a gauge, however, the gauge is non conductive, it would not be a safe practice for a HI to do, inside of any panel. Sometimes you can remove the LB cover on the outside of the house and get lucky enough that the wire markings are visible there, too. Otherwise, if you cannot find markings on the wire, nothing else will tell you what the actual ampacity is. Your best bet is not to guess either....but rather recommend it be verified by a qualified electrician.
Now for the main breaker issue. The only thing you should be saying is....recommending that a qualified electrician inspect and determine if the panel is in accordance with local and national codes. If the sparky then decides the panel should be upgraded, it is then on the sparky and not the HI. Don't say anything in regards to a lack of a main breaker to the customer. It is not in your scope of work as a HI. It is though, in the scope of work for a sparky. This way the homeowner can't come back to you, the HI, and say that you are screwed up. All you did was put the decision to upgrade in the lap of a qualified sparky.
This information has been edited and reviewed for errors by your favorite resident sparky.