Terminal block amp rating

Capn_Tom · Post by **Capn_Tom** » Fri Apr 03, 2009 7:44 pm

Is the amp rating for a terminal block the maximum per circuit or for the total of all circuits?

Curmudgeon · Post by **Curmudgeon** » Fri Apr 03, 2009 8:16 pm

Your timing is perfect! I read an article about this very topic just the other day but had to wait for the little "hampster-on-the-wheel" to wake up before I remembered WHERE I read it. The April 2009 issue of Cruising World included the first of a 2-part article on upgrading an older boats' electrical system ("Sparky Takes Stock"). The article states that "With a bus bar, you must consider the total cumulative amperage that you might pull through the bar if all of the circuits attached to it operate simultaneously". The test subject in the article is a '78 Sabre 34 and for the DC negative return points they were upgrading to bus bars with a rated ampacity of 150 amps. As for circuit breakers, the article goes on to say "ABYC allows us to rate them at up to 150 percent of the ampacity of the conductors they're intended to protect. In other words, technically you could specify a 15-amp breaker for a circuit drawing 10 amps, but in reality, it's much more common to choose a breaker that matches the load, or is rated just slightly higher, say, for example, a 10-amp breaker for a 8-amp circuit".

LazyGuy · Post by **LazyGuy** » Fri Apr 03, 2009 8:23 pm

Curmudgeon,

I feel compelled to correct your final statement. The breaker is to protect the wire, the wire is sized to the load. If you have an 10 amp (max) load, Use AWG 12 that is good up to 15 amps and protect the cable with a 15 Amp breaker.

Curmudgeon · Post by **Curmudgeon** » Fri Apr 03, 2009 8:30 pm

The italics are direct quotes from the article, but perhaps just including snips of the article put it out-of-context. If you get a chance, read the article and let us know if there are indeed errors or omissions.

Popeye1865 · Post by **Popeye1865** » Fri Apr 03, 2009 9:16 pm

LazyGuy wrote:Curmudgeon,

I feel compelled to correct your final statement. The breaker is to protect the wire, the wire is sized to the load. If you have an 10 amp (max) load, Use AWG 12 that is good up to 15 amps and protect the cable with a 15 Amp breaker.

don't forget about total length of wire run 12awg may be fine for a short distance but 15@at 60ft will require a much larger conductor. there are many factors that go into choosing what elect components are right for the application. there are many parameters to be met to make a good system be careful not to over simplify.

Back to the original question "Is the amp rating for a terminal block the maximum per circuit or for the total of all circuits?" If you are truly referring to a terminal block/strip than the amp rating is for each individual circuit, on the other hand if you are referring to a buss bar than than the amp capacity applies for the whole unit
hope that helps

Brandon

Capn_Tom · Post by **Capn_Tom** » Fri Apr 03, 2009 9:42 pm

Yes I was referring to a terminal strip. It was actually the Cruising World article that led to my question. I am finally starting to pull wires tomorrow and when I pulled out my Blue Sea terminal blocks I noticed the 30 amp rating which led me to recall the 150 amp rating referred to in the article. I was fairly certain it was a circuit max since Blue Sea's largest is 65 amps.

Thank you for the clarification!