Electrical Insights?

Ashraf Farrag · **Posted:** Mon Oct 04, 2004 11:06 am

I need to do a "little" re-wiring in the garage (which is attached to my house) to accomodate some 230V devices. My main breaker panel is in the garage and is currently full. I filled the last slots installing one to run my air compressor. I need room for another breaker...so...

My plan/thoughts as of now:
Remove breaker for air compressor from current panel
Add breaker to current panel for combined load of air compressor and extra 230V outlet
Install second panel next to main panel
Run appropriate gauge wire to conduct the combined load from breaker in main panel to bus bars of second panel
Move compressor wiring and wire 230V outlet #2 (with appropriate wiring for it's load) to new panel

Thoughts?

Anyone know if this actually requires dealing with Durham County gub'ment? Anyone got a recommendation for an inexpensive electrician if that is the case (or someone in the club who is one)?

I'm not pulling a new panel from the main electrical feed (which is how I interpret their form of things requiring a permit). It doesn't make sense that one would have to get a permit to add another circuit to an existing panel ("essentially" what I'm doing, but I could be wrong).

Thanks and regards,
--Ashraf

Donnie Barnes · **Posted:** Mon Oct 04, 2004 11:10 am

You won't need a permit. Call the electrician we use...Rich Prather (I think you've met him). His crew is doing some work in Durham now, so swinging in for something like this shouldn't be a big deal. They're the best electricians I've seen, and they work reasonable.

Rich Prather
918-7549 home
382-4245 pager

Scott Johnson · **Posted:** Mon Oct 04, 2004 12:44 pm

The only problem I can envision is that you may exceed the capacity of the main panel.

I wired my detached garage in similar fashion. I have a 60 amp breaker in the main panel and am feeding a sub panel from that. The sub panel is loaded with a few other breakers... Never had a problem.

I'm also in the city of Durham, and they never complained about the work I did (but I didn't ask permission, and I stayed a Holiday Inn Express).

Scott

Chuck Frank · **Posted:** Mon Oct 04, 2004 2:06 pm

Are you going to be using these devices in conjunction with each other?
If not, replace the hard wire to the compressor with a socket and plug. Just switch the plug for whatever you want to use. If you are planning to use more than one at a time, then the limiting factor is likely to be the wiring from the main (house) panel to the garage panel. Most electricians won't put in any heavier wire than what is required for the subpanel capacity, especially if the garage is detached, since the code requires much more expensive wire, deeper burying, and possiby conduit sheathing for higher loads.
If your subpanel is full because you split the 110V wiring into several circuits, you could always rejoin some of those circuits before they enter the panel to free up breakers, or possibly use stacked breakers (two breakers that take up the space of one in the panel) for a couple of the lighter loaded circuits without needing to do any rewiring. If you are going to be doing this yourself, or to prepare for the call to the electrician, add up the amps needed for all that might be on at once, add 25% more and see if you have exceeded the main panel breaker going to the garage. If so or are close, you may want to consider having a second service line and meter run to the garage.

Adam Ligon · **Posted:** Mon Oct 04, 2004 2:22 pm

Yeah there are several options.

The sub panel you mentioned for one. Also some manufactures make both normal single breakers and 1/2 size ones. I mean you might be able to fit 2 half 's in the place of 1 normal if they are available for your style panel box.

Richard Casto · **Posted:** Mon Oct 04, 2004 4:43 pm

ok, I am thinking about doing some of the same in my garage. I haven't added it all up yet, but just in case, I have a follow up question...

If your main breaker is 60 Amps (not sure what mine is right now), and you want to exceed this, the only option I have seen put forward is to increase this via a line from the street, meter and service box. But how can you tell what amperage rating the existing service is into the house. I am assuming that it is up to the original contractor to decide he is going to put in a 60 amp box even if the line in would support a 100 amp just because it is cheaper for him to do so. I would much rather not have to try to run a second line vs. just replace the panel/main breaker with a larger capacity unit.

DickRasmussen · **Posted:** Mon Oct 04, 2004 5:36 pm

If you have to ask a bunch of car folk who may or may not know what we are doing in regard to the National Electrical Code, your specific situation, and what is available for your current panelboards, etc. you REALLY need to contact a QUALIFIED ELECTRICIAN. I'm serious. I spent 29 years working as a product safety engineer with UL, was on a National Electrical Code "code making panel", was involved with many of the issues and products involved with your question and I won't even begin to "engineer" it over the internet. I could "probably" sort it out if I was physically looking at the situation, had my NEC with me and some other tutorial information, etc. In fact I've done so for my "shop" wiring system. What others have said may be "appropriate" but you really need an "expert" to look at the specifics . . . in person. Too many variables and gotcha's. Note that as Chuck said, IF you have two big loads, like a cord connected 240 VAC air conditioner and a 240 VAC Air Compressor, having them share (One at a time) the same receptacle is a good idea and totally legit . . . been there, done that. Ditto for other loads.

In regard to Richard's question about service capacity: Take a look inside the main panel (closest to the meter). It may have a rating label inside. Also look at the main breaker size in that panel. Again, lots of variables which require someone who understands this stuff to sort out.

Dick

Adam Ligon · **Posted:** Mon Oct 04, 2004 11:13 pm

Here's a little homework for everyone. Go to you panel right now and add up all the various breakers. Guess what it wil be much more than the 100 or 200 amps your panel is 'rated for'.

Why because you will never use all of them at full power at the same time. And guess what if you do they will trip, go figure. That is the whole point of a circuit breaker.

Tha being said yes do not just wire in something without knowing what you are doing. But there have been many goo dsugestions in this thread as for options.

Carl Fisher · **Posted:** Tue Oct 05, 2004 7:40 am

Adam Ligon wrote:

Here's a little homework for everyone. Go to you panel right now and add up all the various breakers. Guess what it wil be much more than the 100 or 200 amps your panel is 'rated for'.

Chuck didn't say "add up your breaker ratings", he said

Chuck Frank wrote:

add up the amps needed for all that might be on at once, add 25% more and see if you have exceeded the main panel breaker going to the garage. If so or are close, you may want to consider having a second service line and meter run to the garage.

So I think you 2 are on the same side here.

DickRasmussen · **Posted:** Tue Oct 05, 2004 9:28 am

As several folks have pointed out the connected load to a circuit or panel can be higher than the ratings. The "problem" is that there is a complicated system for sorting this stuff out. Also, the maximum circuit breaker or fuse size for a branch circuit cannot exceed the ampacity (current) rating of the conductor. Conductor ampacity is rated based on material, size, and insulation temperature rating. You should NOT increase the current rating of a branch circuit overcurrent protection device (circuit breaker or fuse) UNLESS the conductors happen to be rated for the new, higher rating (unlikely in a home wiring system). Any replacement or new circuit breakers put in a panel must be Listed for the specific panel. Some will physically interchange but they won't necessarily be Listed for use in the Panel you have. You need to look at the label info on the panel and on the breaker to sort out interchangeability. The major concern with all this stuff is heat in the panel and heat in your walls during either heavy load normal operation or during overload situations or faults (shorts, etc.). Excess heat = fire department.

Dick (Registered Professional Engineer)

Adam Ligon · **Posted:** Tue Oct 05, 2004 10:46 am

And that is why there is a main breaker for the whole box. So if the total load goes over the rated current it trips all the power. I never said anything about touching it. Nor am I saying anything about replacing breakers with higher ones. That would be dangerous and unsafe.

Chuck Frank · **Posted:** Thu Oct 07, 2004 5:24 pm

Breakers should be considered a safety device of last resort, not loading it up until it blows is OK. (NB: I am not a licensed electrician or engineer, but I did work as an assistant to one for a year in college under work-study, and have rewired my entire house with much study of the code and checking by a licensed electrician)
If the wiring is marginal (especially older homes or ones with aluminum wire that was used for a short while), has a poor splice or device connection, a chafed wire or some dumbass has put in a heavier breaker to stop having to reset an overloaded circuit, you can have a safety and fire issue without tripping the breaker. IMHO When it comes to electricity, it's much safer to err on the conservative side. The main reason I rewired my house is that it's a 1930's vintage, which was updated to 220 service and breaker panel when central air was added in the 60's. The problem I discovered is that the electrician took the easy way out and ran feeds from the new panel in the basement into the old 4 circuit screw fuse panel in the kitchen cupboard using it like a giant junction box after stripping out the guts. So the rest of the house was still wired with the old BX cable on three circuits. When I went to change out worn wall sockets and switches, the old insulation and even the wire itself would just crumble in my hands. :shock:

One thing to think about when it comes to garage wiring, electric motors and heating devices usually draw a whopping amount of current at startup compared to what they draw while running, so it is best to not use your wall switch to turn on a lot of devices at once. I have been in garage/shops where when we walked in the owner turned on the wall switch and a bunch of machines started running as well as the lights coming on. :roll:

THSCC Forums

Electrical Insights?

Who is online