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# Electrical circuit question

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• May 21st, 2018 11:50 am
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[OP]
Apr 10, 2009
1299 posts
Hamilton

## Electrical circuit question

Whenever I have added a circuit in the past I haven't been too worried about overloading a circuit because I usually severely underestimate the load on a given circuit/breaker. I.e. adding 2 receptacles and 1 light. However I am curious as to how to properly add up potential devices on a given line.
Lets say I'm planning a rec room with 3 TVs (each with cable boxes) - some extras like Roku, BD Player, and of course charging of phones. Where would I start to see how close I am to being over loaded?
I get looking up the specs of the TVs, boxes, etc but I get confused with the Watts/Volts/Amps conversion.
Any direction or help is appreciated.
12 replies
Jul 3, 2017
2707 posts
Those devices would not typically use a significant amount of power. The big power hogs are things with motors and heating coils, e.g., kitchen appliances (which is why your kitchen plugs are often doubled up on a 30-amp breaker).

Power conversion is simple enough. To get amps, divide watts by volts, so for example a TV that uses 300 watts maximum would require 300w/110v = 2.7 amps. Add up all the amps from all the sockets connected to one breaker and make sure it doesn't get too close to the breaker maximum (e.g., usually 15 amps).
[OP]
Apr 10, 2009
1299 posts
Hamilton
Exp315 wrote:
May 18th, 2018 10:23 am
Those devices would not typically use a significant amount of power. The big power hogs are things with motors and heating coils, e.g., kitchen appliances (which is why your kitchen plugs are often doubled up on a 30-amp breaker).

Power conversion is simple enough. To get amps, divide watts by volts, so for example a TV that uses 300 watts maximum would require 300w/110v = 2.7 amps. Add up all the amps from all the sockets connected to one breaker and make sure it doesn't get too close to the breaker maximum (e.g., usually 15 amps).
I guess that's where I'm going with this... if a TV is 2.7 amps x3 I'm already at more than half of the 15. Add in the rest and theoretically I could be getting close.
Dec 10, 2008
3848 posts
Toronto
15a breaker means you only have 12a to work with because of the 20% rule

How many lights and receptacles do you have on the breaker right now?
[OP]
Apr 10, 2009
1299 posts
Hamilton
RCGA wrote:
May 18th, 2018 11:07 am
15a breaker means you only have 12a to work with because of the 20% rule

How many lights and receptacles do you have on the breaker right now?
it would be a new breaker. sounds like this room should be split with a second circuit not drawing as much.
[OP]
Apr 10, 2009
1299 posts
Hamilton
soupmaster666 wrote:
May 18th, 2018 10:16 am
You would use the rules in the electrical code. You might be able to find details on Google, using the section number 8-304

Fortunately it is not legal to add new outlets or other fixtures without a permit and inspection, so if there are any problems they will be caught.

For your last note, Amps * Volts = Watts. If you have a 15-amp breaker, and your outlet is 120 volts, that means the breaker will trip above 1800 watts.

It is slightly more complicated than that, because Watts actually equals Amps * Power Factor * Volts, but you can just throw in 20% or 30% overhead.

Of course, all parts of the Code apply, such as not exceeding 70% or 80% of the breaker's rating (commonly 12 Amps or 1440 Watts).
Only issue I have with inspection is that I'm afraid the inspector will comment on other things done before I bought the house. (Hot tub, outdoor lighting). I want to get an inspection (I already have a building permit) but I don't want to open a can of worms on previous work. Nothing looks shoddy, its all new, stapled, etc. I'm just not sure how tight these inspectors are with stuff you aren't actually calling about. Its a 7 year old house so its not a massive can of worms.
Dec 10, 2008
3848 posts
Toronto
Inspector won't GAF about previous work unless it's done so poorly that they can't help but notice.
Sr. Member
Mar 3, 2013
514 posts
East Gwillimbury
I never understood why the general public is so afraid of inspections. Did something happen at some point in time when an inspector opened a can of worms for a homeowner?
The only time I have ever heard of an inspector giving a homeowner a hard time is when they are caught working without a permit or hiring someone under the table.
Inspectors walk in, have a look at the work to be inspected and leave. Unless there is some immediate danger or serious electrical hazard, they really don't give a damn.
[OP]
Apr 10, 2009
1299 posts
Hamilton
MrSparky wrote:
May 18th, 2018 3:28 pm
I never understood why the general public is so afraid of inspections. Did something happen at some point in time when an inspector opened a can of worms for a homeowner?
The only time I have ever heard of an inspector giving a homeowner a hard time is when they are caught working without a permit or hiring someone under the table.
Inspectors walk in, have a look at the work to be inspected and leave. Unless there is some immediate danger or serious electrical hazard, they really don't give a damn.
I'm not at all afraid of an inspection. Just didn't want to get nailed for work I didn't do. I've had multiple building inspections in the past. They're generally good people happy to help.
Sr. Member
Apr 6, 2008
570 posts
CaptainCrash wrote:
May 18th, 2018 3:59 pm
I'm not at all afraid of an inspection. Just didn't want to get nailed for work I didn't do. I've had multiple building inspections in the past. They're generally good people happy to help.
Remember that ESA is a government (provincially) run corporation and everyone is a public servant. Take that for what you will when you are thinking that they will go over and above the bare minimum with their job...
Jan 19, 2011
2610 posts
CaptainCrash wrote:
May 18th, 2018 9:22 am
Whenever I have added a circuit in the past I haven't been too worried about overloading a circuit because I usually severely underestimate the load on a given circuit/breaker. I.e. adding 2 receptacles and 1 light. However I am curious as to how to properly add up potential devices on a given line.
Lets say I'm planning a rec room with 3 TVs (each with cable boxes) - some extras like Roku, BD Player, and of course charging of phones. Where would I start to see how close I am to being over loaded?
I get looking up the specs of the TVs, boxes, etc but I get confused with the Watts/Volts/Amps conversion.
Any direction or help is appreciated.
You do nothing of the sort,

You follow the Ontario Electrical code, which clearly states that a total of not more than 12 devices (standard duplex receptacles or light outlet boxes) can be connected to one 15 amp circuit.

You do not need to calculate anything at all, or think about or guess or conjecture as to what you might plug in.

Of course, this is for typical household circuits. knowing that you are dedicating most of the outlets to be used, simply reduce the number of outlets accordingly. I typically wire only 10 devices per circuit, six or seven receptacle outlets at most, the balance made up of octagon boxes for lighting. I never trip breakers...
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
Deal Fanatic
Jan 6, 2002
5281 posts
Toronto
MrSparky wrote:
May 18th, 2018 3:28 pm
I never understood why the general public is so afraid of inspections. Did something happen at some point in time when an inspector opened a can of worms for a homeowner?
The only time I have ever heard of an inspector giving a homeowner a hard time is when they are caught working without a permit or hiring someone under the table.
Inspectors walk in, have a look at the work to be inspected and leave. Unless there is some immediate danger or serious electrical hazard, they really don't give a damn.
My experience with ESA inspectors has been nothing but positive. As others have mentioned, they are there to inspect the change and to make sure you know what you're doing.

I get the sense that for homeowners doing their own work, once they know/see you're not trying to cut corners and you are trying to do the right thing, it's a win-win dialog. When I was doing my kitchen, the ESA guy took the time to explain why/how a particular part of of my rough-in was wrong. Not just that it was wrong, but the explanation of why the rule was in place at all and what it was trying to accomplish/mitigate: not just what but why.

When inspecting my basement work, the ESA inspector also casually pointed some preexisting things out "you should probably fix that eventually" but they weren't immediate life hazards. I would imagine if they saw open splices or other true immediate life safety or fire hazards, they probably have to do something, sure.
Revolutionary times must on occasion make do with considerable abridgements in order to accentuate the political line more strongly.
Deal Fanatic
Jan 6, 2002
5281 posts
Toronto
fieldhousehandyman wrote:
May 18th, 2018 9:19 pm
You follow the Ontario Electrical code, which clearly states that a total of not more than 12 devices (standard duplex receptacles or light outlet boxes) can be connected to one 15 amp circuit.

You do not need to calculate anything at all, or think about or guess or conjecture as to what you might plug in.
That's good advice strictly from a compliance point of view. But it makes sense to look at your own real world load scenarios if you know they are going to happen, and design around that.