A 10/3 wire from a garage subpanel connected to a 30 amp twin breaker was installed into the main panel without turning off the main power. The breaker arced made a noise, but did not rip. Was this because of the install without shutting off the power or is there something else as well?
It sounds as if the load was connected and the breaker was turned on when installed. Installing a breaker with a live panel is not uncommon for a qualified electrician. The electrician would not have the breaker wired or turned on when installing because this could cause an arc.
Thanks for all the responses, turns out there is a problem with the panel box and we will be spending a large sum to replace it. Bought this house a couple of years ago, just one more thing added to a list.
Bruce is an electrician who sometimes has helpful advice on this forum. If he answers, you will have some explanation. However, in the meantime, why doesn't the apprentice give his journeyman boss a call and ask about this? Surely, if he is training as an electrician, he has access to someone who can help him explain what has happened and who will know if there is any real problem.
He stays with us when here ...is otherwise working/learning in another city and will not be back till mid Sept .The event was scary so we said just leave - finish next month . We are just feeling unsure of this and have read that electricians sometimes do work on live panels .....and if that is the case how can this " arc " which seemed significant - be the only cause . The prewire was ok'd -inspected . It is worrisome if one doesn't know . Can the breaker have been faulty ...is the breaker know blown or something ...can there have been a problem with the panel box ? The house is only 12yrs old all electrical has been done by pros . One would assume that all is to the most recent code .
It's sounds like you connected your neutral to your positive
