Circuit Breaker for 50 amp Control Panel

[ontum]

Hello,

I am in the process of building a 50 amp BCS control panel in my brew shed. I've noticed in several builds, that a 50 amp spa panel is used to power their control panels with two 5500 W elements. I spoke with an electrician at my work and asked him about my power needs. I informed him I would be using about 44 amps and he mentioned I would need a 60 amp breaker because you can only put a constant load of 80% on a breaker. 44 amps is 88% of a 50 amp panel and to be up to code a 60 amp breaker is needed.

I could be missing something as I am figuring this all out for the first time, but I think some people are not adding a big enough breaker in their panel. Am I incorrect in my thinking? To be safe, I put 60 breaker in my main panel, ran 150 feet of cable underground to my brew shed, and put in a 60 amp GFI spa panel.

-
Craig
Spa panel by ontum, on Flickr

 

[Bill_in_VA]

It's because brewing isn't a constant load...

 

[Facinerous]

There is a difference in ratings between what is considered continuous and not.

Beside that, I believe the electrician is using a generic rule of thumb when designing circuits for a home or other system. It does not mean that you HAVE to use that rule. As a matter of fact the wire that you are using is already de-rated by a value to make sure that those pushing the limits of circuit wire ampacity are still within safe limits.

An example is the simple #12 wire. In reality you can safely push 30 amps through that wire without ill effect, but the National Code limits that wire for generic branch circuit use to 20 amps. There are many factors that would need to be considered in order to size wiring. So the best practice is to use what is standard rather than try and push it.

I would never recommend to another person to use a wire size that is smaller than what the NEC states. That goes for breaker rating as well.

One thing I would recommend is checking that that 50Amp spa panel is indeed rated for 60 amps. There are bus bars that you need to be aware of as well.

As after being long winded I will directly answer your question and say, the electrician is not entirely wrong. But that is with regard to being an electrician and building a house or building where you don't know what the plugs are going to be used for. In your case a 50 amp breaker would have been fine because you already know how much load you will be putting through that circuit, and it is intended for a single purpose.

 

[jca]

Is there any safety downside to having a breaker too small? The breaker should just not be larger than the wire attached to it can safety handle without getting too warm.

 

[Onkel_Udo]

Is there any safety downside to having a breaker too small? The breaker should just not be larger than the wire attached to it can safety handle without getting too warm.

The way to think about it is a current over protection device (a standard breaker is one of these) is designed to protect the wire...not the items hooked up to it. So "too large" wire is not an issue.

 

[Facinerous]

The downside to a breaker that is rated to small is it will trip at inconvenient times, or just right away. There is no safety concern though.

Onkel is right, the wire can be 'size huge' compared to the breaker rating and that would be fine. It comes down to cost of wire.