When to add a new circuit?

Factual Questions
1

I am thinking of adding a couple of electrical outlets to the den. Right now there are 5 outlets (plus a ceiling light) on two 15-amp circuits. Currently I have 3 computers, two printers, a scanner, couple of desk lamps, shredder, router, battery chargers, and maybe a couple of other odds & ends. The router and one computer are on all the time, the rest is used transiently. We also have a 1500W ceramic heater that gets occasional use. We are getting built-in desks and shelving installed. Eventually I will be adding another computer plus about 400 watts of desk lighting. I would like to add 4-5 outlets accessible from the upper cabinets. I do not want to overload the circuits, however (I am concerned about the heater). I know how to wire switches and outlets (to code) but I do not know how to add another circuit. The basement is finished so running the wire might be a little tricky.

Are there guidelines for how much of a load to put on a circuit? I would think you would want the max load to be some percentage (less than 100) of the rated load for the circuit.

How do I know whether I need to call an electrician to add a new circuit?

2

Each circuit should be rated for 10 amps. (If you’re not sure, take a look at the circuit breakers in the basement. They should say “10” on them somewhere.)

From everything you plan to add, it definitely can’t hurt to add another circuit. It’s not hard to add a circuit to the breaker panel, but running the wires without tearing the walls apart may be difficult. If you don’t have experience, you should probably call an electrician.

3

UK electrical regulations may be very differant to the US, especially because all our domestic supplies run on 220V, and every single appliance has a fuse built into the plug, which I belive is differant to the US where in the case of 110V circuits you just use 2 pin unfused plug.

That disclaimer being made, what you first need to consider, is what we in the UK call electrical diversity, that is, the number of appliances that will be energised at any time, which is not the same as the worst case scenario of everything being switched on.

Think about which circuits lead to which outlets, and then add up the wattage of all appliances likely to be running from it.

Next, you need to look at the number of outlets you wish to add, and sum in the wattage that these will be supplying.

Add both these figures together, and divide this total, by you supply voltage, ie 110V, and this will give you the current that you are wishing to draw from the circuit.

Your next issue is to consider the cross section area of your circuit cables, now you in the US use a.w.g whereas we in Europe use mm[sup]2[/sup] square millitmetres.
Since I don’t have the chart available, you will need to look this up, there will definately be something on the net.

Your circuit wiring obviously needs to be able to carry this current continuously so if they are running at or near the limit for the size of your supply cables, then it a case of running a comlpetely fresh circuit from your distribution board.

Personally, I would not be wanting to run a large heater such as you describe on the same circuit as IT and electronic equipment from the same circuit, in fact, looking at your current total applainces, I would say that you really should consider running another circuit completely.

It is much more than a matter of looking at your normal operating current, you would also need to consider what happens when fault conditions occur, the nominal gauge of supply wires from current delivery consderations is usually enough, but not always, sometimes you may have to use a wire size larger than you would expect due to special requirments such as long cable runs - above 50-100 yards, or going through very warm environments such as near a house furnace.

I have left out considerations about the fuse disconnection times and circuit impedance as your electrical system is such that a US poster would be better advised, but in my experience, you can get away with a whole lot more if you use GFCI devices as they tolerate a much lower level of fault current than do fuses and so they disconnect much faster.

4

Excuse me, what?

5

To help you out here in case you aren’t aware, amps x volts = watts

So your 1500watt heater is drawing 13.6 amps all by itself. In theory it should be on its own 15 amp circuit.

It is your biggest problem.

Two circuits would be plenty for all your lighting and computing needs but when adding in the heater you’ll probably find your total wattage will exceed the 3300-3600 watts total those circuits can handle.

As the electrical coding already takes into account the saftey of the wire ie it not overheating under its spec’ed load. Your main concern is blowing the circuit breakers.

Depending on your situatin with the desks and such, I would try with what you have already and if you find you are blowing the curcuit breaker get rid of the heater or add another circuit.

To add another circuit you need to run wire from the main panel to where you want it. Remember when running wires it is just as easy to run 2 as it is one so if you see more energy needs in your future at least run them and cap them off so they are there.

6

Um, if you’re going to run common 14 gauge wire, use a 15 amp breaker. For 12 gauge wire, use a 20 amp breaker.

7

Those are the budget electrician circuits, run with 16 or 18 gauge SJ, or maybe zip cord. :wink:

8

Heh. Well, I haven’t even seen a 10 A breaker in a residential installation for at least 10 years, which is why I was surprised by that post. They’re not at all common anymore; 15 A is the smallest rating I ever deal with.

9

Oops, I meant 20 amps. It’s been a while. :wink:

10

True, but where can you even buy a 10 amp breaker? Fuses, yes … breakers, not so much.

For the OP, lose the space heater or add a dedicated circuit just for it. With all that you plan to operate in this room, an additional circuit isn’t a bad idea. You’d hate it if someone plugging in a vacuum cleaner tripped the breaker and shut down your computers.

I’m sure an honest-to Og electrician will come along to correct me, but all of the loads on a circuit should not total more than 85% of the circuit rating.

11

On a 15 amp circuit, you can have up to ten receptacles, and up to thirteen on a 20 amp circuit. The NEC doesn’t simply say this, but those are the numbers that you’ll arrive at after calculating out their watts per device per circuit formula.

If it’s normal for you to have an electric space heater in the room, I’d dedicate a 15 amp (or even a 20 amp) circuit to just that one receptacle. When it’s not running the heater, it’ll be a fine place to plug in the vacuum cleaner. (I’ll bet your vac proudly proclaims a surprisingly large number of amps on its label - probably anywhere from 10 to 13 - and it’ll be more than happy to overload a circuit that’s got other things running.

12

Oh, they’re out there. Not something you can generally walk into your local electrical supply store or Home Depot and pick up off the shelf, though. Most of the time, they’d need to special order one for you. I’d never bother with one nowadays, even when running a branch circuit for lighting only.

13

Much useful advice here, I’ll address my info to this post.

There are currently 5 receptacles plus the ceiling light. The ceiling light and two receptacles are on one 15-amp circuit, and the other three receptacles are on another 15-amp circuit. With your rule of thumb I could have 20 receptacles, room to add 14. I want to add maybe 4.

I have a Hoover upright that pulls 5.0 amps. The heater is used only occasionally, but I’m thinking putting it on another circuit is a good idea. However, as noted, running the wire would be a bitch. The den is directly over a finished part of the basement on one corner of the house and the main comes in at the opposite corner of the house. Wish I’d thought about this before we had the basement finished.

Another option would be to tap into the circuit of the room next door, which is the living room and just has two lamps that we almost never use anyway.

14

You should add another circuit (or two), if you can.

To figure out if you can:

  1. look at your house circuit breaker box, and see it there are empty spaces where you can add another breaker. If not, it’s going to be trickier. (And you need to take the cover off to be sure – some boxes have the removable slots looking like open breaker spaces, but the actual bus bar inside the box doesn’t come down that far.)

If you don’t have any open spaces, you might be able to replace an existing breaker with a double breaker (2 separate thin breakers that fit in the space for 1 breaker), but those are a bit more expensive, and require more work (plus throwing away the old breaker). Or you need to add a sub-box, with more breakers, and move some circuits there. Or replace your current main box with a bigger one with space for more breakers. Either of these options probably requires a licensed electrician.

  1. Look to see if there is an accessible path from the breaker box to where you want the new circuits. You’ve done this; the answer is semi-bad: the path is there in the basement, but you will have to remove some finishing to get at it, and then replace that.

  2. Look to see if you have the skills to do this. Most of it is pretty easy, and not very risky – all the new wiring is dead electrically until you connect it to the new breaker, and only when you are working inside the breaker box will you be around live circuits.

You should try to get that heater onto it’s own circuit. Especially try to not have it on the same circuit with your computers & other sensitive electronic stuff. (Though a heater isn’t nearly as bad as a motor for this.)

Tapping into the circuit of the room next door is certainly feasible, if there is unused circuit capacity there. But the mechanics of actually doing that may be tough to do without messing up your walls in both rooms. (Be sure to mark this on the circuit board, to prevent sometime in the future somebody turning off the 2 breakers for this room, and thinking all the outlets are dead, not remembering that some are powered from the living room circuit.)

I think DancesWithCats was joking, but it’s certainly NOT LEGAL and not safe to run zipcord inside walls.
And special-ordering a 10A circuit breaker and wire for it would probably cost you more – just use the standard 15A breaker and #14 NM cable. That’s on sale ever couple of months anyway. Most of the work here will be running the wires around the house; that’s the same effort whether it’s a 10A or 15A circuit. (Even running wires for a second circuit is very little additional effort once you’re in the walls & basement ceiling, so you might as well put in 2 circuits while you’re at it.) Also, adding extra receptacles is very little additional work or expense when you’re doing this wiring, but much harder later. Make all those outlets you’re planning double-gang boxes, with 4 plug-ins in each – it’ll only cost you about $10 more for the room, but you’ll really appreciate it over the years.

15

I don’t have a cite, but there is a limit to the number of double breakers allowed in a panel. I THINK it’s 2.