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#209775 - 04/24/13 10:28 AM Question about panel capacity
Darren Offline
New Member

Registered: 04/24/13
Posts: 4
Loc: Ontario, Canada
I have a Siemens panel (I don't have the model number in front of me). I've read all the labels. It says its max rating is 125Amp, it had places for 24 full sized breakers, and the label states it supports max 48 circuits. The bus/bars in the panel all support 48 lines as well.

Does this mean that I could theoretically use tandem breakers in each location? How else could it reach 48 circuits? Currently there is only one tandem breaker in my panel.

I'm in the design phase of a huge basement renovation and I'm running out of circuits. I have 4 full size locations available for me to use in my basement (the washer, dryer and furnace are are other circuits).

I'm adding a jetted tub, so that's one circuit. I'm adding a lot of recessed/pot lighting, so that pretty much ties up another circuit. The bedroom will require an AFCI circuit, so that is another one tied up, and AFCI's are usually full size breakers. There are various GFCI requirements for the bathroom, and then all the other lighting and plug requirements... And I'm adding hydronic infloor heating, so I'm guessing that the pump for that system will likely require its own circuit as well.

I might... might be able to squeeze it all to the 4 full sized slots, but it would be extremely tight.
The reason I'm looking at the tandem breakers is because I do not what to upgrade to a larger panel or branch off to a sub panel. I am thinking I could replace one or two of the full sized 15A breakers with tandems.

Also, when I get the full electrical layout drawn up, can I post it for critic? This is by far the largest wiring project I have ever done, and this will be going through all inspections.


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#209776 - 04/24/13 02:12 PM Re: Question about panel capacity [Re: Darren]
Chuck11 Offline
New Member

Registered: 04/15/13
Posts: 2
Loc: Canada
Hi Darren,
Yes, if the label states it has 48 poles then the panel should be able to accommodate tandem breakers in each "full breaker" position (giving you a possible 48 circuits total).

You mention that the panelboard's mains are rated for 125A, it shouldn't be an issue but I would complete a load calculation to ensure the panelboard won't be overloaded. Additionally, use the load calc to ensure the panel's feeder and overcurrent device (if any), protecting the panelboard can handle the increased load.

As you've suggested, you could change out some of the full size breakers and replace them with tandems if you need some extra capacity. There are a variety of options for tandem breakers to consider, for example;

A 15/30/15 tandem breaker would take up two full breaker positions but could be used for two 120V, 15A circuits and one 208V-single phase 30A circuit (for your dryer perhaps).

I'm unfamiliar with Ontario codes but it may be worth while to inquire with your local inspector regarding use and quantity of tandem breakers, before you get too far down the road.

#209777 - 04/24/13 04:58 PM Re: Question about panel capacity [Re: Darren]
Darren Offline
New Member

Registered: 04/24/13
Posts: 4
Loc: Ontario, Canada
Hi Chuck11,
thanks for the feedback.

I will be doing a load Calc for sure. I'm juggling everything at once. My road block right now is waiting for my permit to get approved, then I'll have a specific inspector assigned to my project. I'd prefer to talk to the same person about this instead of talking to different people.

I just took a closer look at my service... and I have to admit, i dont know much about anything behind the panel.

My main service/cut-off is labelled as a 100amp service (2 pole, 3 wire). It has two 100Amp one-time fuses.
So I guess that means I'm limited by 100Amp... but isn't that 100Amp per pole?

Bottom line, I'll do some more reading, and speaking with an electrician as well my inspector about these details.



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