Which circuit breakers?

Cardiffcruiser

Cardiffcruiser

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Hi all,
I've traced various faults with my boat electrics back to faulty circuit breakers which have evidence of corrosion - and gave some strange faults!

3 out of 8 cb's are faulty.

I now need to replace these, however I'm need some guidance in 3 areas:-

1. the faulty ones are made by ETA, but the ETA ones are twice the price of those from ECS - are they worth the extra money (especially after 3 out of 8 have failed on an 8 year old boat)? Are all cb's like this the same quality?

2. How do you calculate the correct rating? the failed ones give max voltages on the side but not their rating - very unhelpful
I have some electrical knowledge and would guess that it's a case of getting the wattage of the system concerned and transposing P=IV to find the current used then adding a margin to prevent nuisance tripping. i.e. a VHF set which transmits at 25w would be 25/12=2.01 therefore cb around 2.5A would be fine - is this right? If so how much margin?
I need one for my interior cabin lights (2 x 15w and 1x 10w wired in parallel), one for my Raymarine st4000+ and a third for my Shoreline VHF.

3. As cb's are quite expensive are they really worthwhile? would a fuse and a switch be better? Do they normally fail after only 8 years?

Thanks.
 
Cannot comment on the various makes of CB .

You are right about calculating the rating in amps from the power in watts ( Amps = watts/volts) but you are wrong about the rating required for your VHF radiotelephone.
It may transmit at 25 watts but its power consumption will be rather more. IIRC my VHF has a 6 amp fuse (recommended) in the supply. 6 amps would therefore be the correct CB rating for that. For items of this nature consult the instruction book to find the correct/recommended CB or fuse size.
 
Quote:
As cb's are quite expensive are they really worthwhile? would a fuse and a switch be better? Do they normally fail after only 8 years?
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If you have a problem on a dark and stormy night, try fumbling around with a torch and fuses rolling all over floor and trying to read what they are rated for, then removing the old one that want's stay put.

The alternative is "press reset" done.

We have several breakers on boars but only 2 sizes and carry one spare for each. have never had on play up or fail in over 10 years. All tested avey three months as per ships log maintenance log.

Avagoodweekend......
 
Vic is correct in his comments on the VHF set. The output stage for the trasmitter will only be 60% or 70% (maybe) efficient. You have still got to power the driver stage and all the other circuitry. In other words, to generate 25 Watts RF power you might need 50 or 60 Watts of electricity going into the set. Hence the 6 Amp fuse in lots of VHF's...
 
Well the raymarine manual reccomends a 12A CB, so that one is sorted. Thanks to you guys - 6A for the VHF.

And I reckon about 4A for the lights?
I think i remember from my apprenticeship long ago that you add currents in a parellel circuit?? giving 40W/12V=3.33A plus a margin gives about 4A?
 
Yes for a number of lights all in parallel add together all the watts then work out the total current.

Four 10 watt bulbs makes 40 watts so the current will be between 3 and 4 amps. I would not "fuse" them at less than 5 amps but the critical element is the cable size.
A fuse or mcb should always be sized below the max safe current rating of the cables in the circuit(s) it is intended to protect. This has implications if a number of circuits are wired to the same fuse or mcb! All the cables must be able to withstand the current that that fuse/mcb will allow.
 
[ QUOTE ]

1. the faulty ones are made by ETA, but the ETA ones are twice the price of those from ECS - are they worth the extra money (especially after 3 out of 8 have failed on an 8 year old boat)? Are all cb's like this the same quality?


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Our 1990 Moody has 8 ETA circuit breakers fitted when the boat was built. All work fine though the cabin light switch is getting quite stiff. Are you sure yours aren't getting damp somehow.
 
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Are you sure yours aren't getting damp somehow.

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I thought the same as there is visable signs of corrosion. However I've soaked the coachroof all around the area outside where the panel is mounted with a hose for a good 20 mins and there is none getting in anywhere in that area (or any other), even after a few hours. We do get some condensation in the boat generally, but there are no water marks or other indications in the area. Can't think of anything else to check.
 
If you want to use them for switching as well as protection then we used 'Heinemann' from whom you can specify CB's to suit exactly your requirements as they make them to order at no greater cost then the off the shelf boys though they take a few weeks to come through. If just for protection then we used Merlin Geran CB's which are spec'ed for dc use. Heinemann do a great brochure on the subject and can easily be contacted.
 
It's sorted!!!

I had originally decided to make a new switch board using switches and fuses, as I couldn't find the CB's for less that £19 each which I though too steep. Though Oldsaltoz is spot on about the pain of finding the right fuse - this made me look a bit further. I've just picked up the exact same ETA 2-5700 CB's that I originally had (and that bainbridge and marine mega store sell for £19) from RS for £7.54 each. Hopefully the end of the problem! Why must the same thing sold for a boat be more than double the price???

Also the current rating was marked on the old ones - it's etched on quite lightly so you have to hold the cb at an angle to the light to read it.

Thanks for the help.
 
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