04:24PM | 04/09/07
Member Since: 11/01/06
34 lifetime posts

I just bought a central vacuum. I need to put a 15A breaker. The unit works on 220/240v. The plug that I have is nema 6-15r.

My load center has come empty slots. I went to HomeDepot and bought a 120/240v circuit breaker. If i put it into the load center, how ill the vacuum know that it is indeed 220v?


Tom O

04:12AM | 04/10/07
Member Since: 09/17/02
477 lifetime posts
If that breaker has 2 places to connect wires, then it is for 240 volt circuits and you have the correct breaker.

The 120/240 volt rating means that the breaker can be used on circuits where no conductor exceeds 120 volts to ground and the voltage between any two conductors does not exceed 240 volts.


09:04AM | 04/10/07
Member Since: 04/25/05
1915 lifetime posts
It took me a while to figure out what your question is.

The breaker is a 2 pole breaker. That is one pole for each leg of the split 120/240 electrical supply.

The service is setup so that each leg is 120 volts from the hot to the neutral and 240 from one hot leg to the other.

For loads such as that vac or air condictioning compressors the load is only 240 volts.

So a hot wire is run to each breaker, plus a 3rd wire for the ground.

Some equipment (mostly dryers and stoves) are both 120 and 240 volt loads. They require runing 4 wires (for new circuits). The 2 hots and a neutral for the 120 and the 4th is the ground.


08:20AM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
thanks for the answers guys!

The load center is a Square-D and the Breaker is a QOT1515. It is a twin breaker with 2 times 15A (there are indeed 2 prongs moving individualy). I think they call this a twin breaker for saving space in the load center.

I understand the principle: the rule of thumb is if the breaker has 2 poles, it's 240v. if it has only 1 pole, it is 120v.

I am not talking about the special breakers for 30A or 40A...

Am I right in assuming this?

Thanks again! You are just a great bunch of people here!


09:32AM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts
The tandem break is two breakers on a single leg of the 120/240. The difference between the 2 terminal is ZERO and it can't be used to supply a 240 load. It only have one connection to the bus bar.

For 240 loads you need a 2 pole breaker.

It will be double wide. Some brands have one common handle. Other have two handles and a factory tie bar tying them together. It has 2 connections to the bus bar. And you can get 240 connecting between the two terminals and 120 from one terminal on the breaker and the neutral.

Here is the 2 pole version.

There is also what is called a quad breaker. It consists of 2 tandem breaker side by side.

It appears that there is none in the QO series, but you can assemble one.

Look down almost at the bottom and find "QOT Tandem Circuit Breakers"

And this note "Order two QOT1515 or QOT2020 circuit breakers and handle tie

Cat. No. QOTHT at $2.50 for common switching of center two poles"

Thsi shows how they are used.

When doing this the two inter breakers are on different legs and you have 240 between them.

This are usefull when you have full panel and can beplace 2 single pole breakers with 2 tandems. The existing 120 loads are connected to the 2 outer termimals and the 240 to the inter two termimals and the tie bar is used on the inner two handles.

NOTE - tandems can only be installed in certain slots as shown on the panel and not all panels will accept them.

Tom O

11:43AM | 04/11/07
Member Since: 09/17/02
477 lifetime posts
I knew I'd get in trouble by taking the easy way out and not properly describing a 2 pole breaker.

Square D's stock number for the breaker you need is QO215.

If you don't have the space needed for this breaker(two full spaces) you'll have to follow Bill's advice & assemble your own tandem breaker as he outlined. If you go that route, don't be tempted to make your own handle tie, use the factory made one.


12:44PM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
ok ok ok ok !

I'm lost here!

Q1. Is the QOT1515 the right choice for running my vacuum? If not, I was under the impression that the 1515 was for 15A 15A so in my mind OK for the vac...

Q2. If the QOT1515 is *NOT* the right breaker, which one should I use?

I'm lost... and I'm not on an island! LOL

Thanks for all your help... and most of all... your patience with me! ;)


03:40PM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts

It takes two full slots.

I suggest that you stop by the library and look at a book or two on wiring and see how 240 circuits are wired.

Look at how an AC is wired.


04:05PM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
Thanks for all your hints!

I did wire the stove... from the load center to the wall outlet and it was so easy to choose the right breaker!

now... i'll go back to HD and buy a new breaker as mentioned.

But regarding the QOT1515... what are they used for? WHat's the difference between a 'tandem' breaker and a regular breaker?

Many many thanks! ;)


05:31PM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts
Tandem breakers are just two independent breakers that will go in one slot.

Some panels need them to full usages.

For example some panels are label 30/40. That means that they have 30 slots, but if you use tandems in 10 of the slots then you can have 40 different poles (ie, 40 different 120 volt circuits).
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