What would it hurt to add 1 or 2 tandem breakers in a 200 amp 40 circuit panel. There's plenty of room for neutrals and grounds. It won't overload the buss, it would be perfectly code acceptable to put 1 or even 2 or 3 - 100 amp sub panel off the same buss, so what does it hurt to squeeze in one more circuit rather than forcing a customer to pay for a sub panel? Don't just point out code referrences that disallow it, but the real harm it could cause. Thanks.
Well Sparky, What good is the NEC if they have black and white rules that sometimes aren't safety issues. I think the NEC is needed and without it and licensing we would have a lot of unsafe conditions created. But an answer basically saying the NEC is the law, right or wrong, and we should abide doesn't cut it with me. Do you ever go a little faster than the speed limit when you drive?
I do agree that you have to draw a line somewhere, but I see more harm in putting 5 - 100 amp sub panels off 1 - 200 amp service than adding 2 circuits to a 40 circuit panel. Yet the 5 sub panels would be allowed.
First The 2 sparky's have, IMHO given very good answers, especially the 1st one. Scott, I also think you are right about the bus, but another reason to think about is the gutter space. Sometimes trying to find where a wire leads to in a panel is dificult at best and unsafe, also heat dissipation is a consideration, and the manufacturers have only tested their panels to these specs. One of the hard parts of being a concerned contractor is the consideration of a customers needs (including financial). If you have 42 existing circuits, and you need 1 or 2 more the dilema is, new subpanel or twin breakers. It can be a tough decision, only you can make. I will ask one more thing - What separates the professional from the nonprofessional?
The average residential panel is generally so lightly loaded at any one time that I don't see it as much of a safety issue. The load on the bus is only going to change by the amount of additional things put on it. You could put 20 subpanels in a 40 circuit panel, and not increase the load at all. Eagle, is there a reason that you can't increase the # to 42 anyway?? Commercial work could be a completely different story, however.