Breaker Sizing

[timm333]

I am relatively new to NEC, and need some help in sizing the breakers for lighting fixtures and non-motor load.

For example, maximum how many 400W Metal Halide lighting fixtures can be placed on breaker of 20A 120V single-phase?

And how many watts of non-motor load can be placed on a 15A breaker at 120V single phase?

 

[dpc]

Refer to NEC Article 220 regarding load calculations the NEC way. I'd advise you to also get a copy of the NEC Handbook if you don't already have a copy.

The NEC distinguishes between continuous and non-continuous loads. Continuous loads must be be accounted for at 125% of their actual loads. For a 400W luminaire, you must determine the input current to the ballast. Lighting is generally assumed to be continuous. So if the ballast draws 450 VA, you must take 125% of this to determine how many can be put on one circuit. Or you can add up the actual continuous loads and use 80% of the breaker rating. But you don't have to do both.

For your second question, the answer will depend on the type of load - continuous or non-continuous.

Dave

David Castor

http://www.cvoes.com

 

[timm333]

I studies NEC 220. There are a few things:

Table 220.12 gives the VA per square foot for lighting. But there is no such table for receptacles. How shall i find the VA for receptacles?

Also, table 220.12 does not tell that how many light fixtures can be placed on one circuit.

Please let me know comments...

 

[waross]

A question from Canada:
Is the NEC handbook similar to the CEC handbook? An explanation and justification for each rule? This is a second book in addition to the basic code book.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

The number of lighting fixtures on a circuit is limited only by the load.

Receptacles are generally taken at 180 VA per receptacle. it is more complicated than that, but that is a general rule.

Bill,

Yes the NEC Handbook contains the complete text of the Code plus explanations and examples, including a lot of illustrations and photographs. it's a good investment. We use the one published by NFPA.

David Castor

http://www.cvoes.com

 

[waross]

Thank you David.
That is very similar to the Canadian handbook. I suspected but I wanted to make the point for any that may have thought that references to the handbook were another name for the code proper.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[timm333]

Just one more question…

Motors have low power factor, so the circuit-breakers for motors are up-sized up to 250% of full load current of the motor.

Light fixtures also have low power factor (due to ballast.) So are the circuit-breakers of light fixtures also up-sized?

 

[dpc]

No.

David Castor

http://www.cvoes.com

 

[waross]

The rated full load current of motors takes the power factor into account. Motors must have overload protection. The breaker provides short circuit protection and is over-sized to allow the motor to start.
The rated current of ballast type fixture includes the power factor of the ballast. The breakers are sized to protect the circuit conductors. The load on the circuit conductors for a continuous load must not exceed 80% of the breaker rating.

Bill
--------------------
"Why not the best?"
Jimmy Carter