Two breakers inline?

Why would the PO of the boat wire these two breakers "in-line"? The cabling on the bus-bar is labelled "capstan" which I presume is for the winches on the boat deck. One breaker is rated 100 amp and the other is rated 50 amps. The windlass has separate breaker.

Jim

is there a chance you can get the pic straight on close like this and then one further back

maybe I am missing something

This is another photo, further back. The breakers in question begin at the top of this photo.

Jim

It appears that they are wired in parallel. The current to the load will be divided through both breakers. The lowest rated will trip first, shift all of the load to the second which will trip if above the setpoint . Go down to one breaker of the appropriate setpoint.

Maybe wanted 150 amp breaker, didn"t have one handy so that happened thinking in parallel you will probably get the necessary amps without tripping either. I don't know enough theory to say why it will of wouldn't work.

High Wire said:

It appears that they are wired in parallel. The current to the load will be divided through both breakers. The lowest rated will trip first, shift all of the load to the second which will trip if above the setpoint . Go down to one breaker of the appropriate setpoint.

Click to expand...

That is what I am seeing

so what amps can you see at the windlass with that setup without tripping a breaker?

I agree with Archie, when the 50 amp trips the 100 amp will not be far behind. Seems like a lot of work to make those short connector pieces (crimp lugs & heat shrink), one breaker may have cost less.

Rafe

I don't know what amps those winches draw/are rated at. One of them failed last summer and I managed to get it "remanned"...
http://www.trawlerforum.com/forums/s31/winch-problem-15631.html

So, what is the best approach? Go to a single breaker? One of these is 50 amp and the other is 100 amps?

I phoned "Blue Sea" and the tech I talked to said the expert on this topic was on his lunch break. I sent an email with the photo and hopefully they will get back to me.

Jim

JDCAVE said:

I don't know what amps those winches draw/are rated at. One of them failed last summer and I managed to get it "remanned"...
http://www.trawlerforum.com/forums/s31/winch-problem-15631.html

So, what is the best approach? Go to a single breaker? One of these is 50 amp and the other is 100 amps?

I phoned "Blue Sea" and the tech I talked to said the expert on this topic was on his lunch break. I sent an email with the photo and hopefully they will get back to me.

Jim

Click to expand...

One breaker only. The winch installation guide should state the required amp value.
Putting 2 breakers in parallel (or series for that matter) has no value. 50 plus 100 does not equal 150 in the breaker world. I'll add that its worse than no value because you will have no idea what load current will finally trip the breakers. Best guess is somewhere north of 100 amps.

JDCAVE said:

I don't know what amps those winches draw/are rated at. One of them failed last summer and I managed to get it "remanned"...
http://www.trawlerforum.com/forums/s31/winch-problem-15631.html

So, what is the best approach? Go to a single breaker? One of these is 50 amp and the other is 100 amps?

I phoned "Blue Sea" and the tech I talked to said the expert on this topic was on his lunch break. I sent an email with the photo and hopefully they will get back to me.

Jim

Click to expand...

I would have and did just use one 150 amp breaker on my boat...but I'm not so sure that your current setup won't work and be just as safe.

Thanks Archie. That can be a spring project. I intend to replace the winches this spring with a Warn model (DC 1200) as per the advice of S3 Systems (Seattle).

Jim

Agreed that what's there is a bad practice. It will completey open somewhere between 100 and 150A, but there is no way to know in advance exactly (or even approximately) where. And it's possible the 50A would trip, but the load continued by the 100A until it trips. Check the manual for the windless or whatever it powers and replace with a single properly sized breaker.

One more thing to consider. The breaker also protects the wire and needs to be sized accordingly. If the winch needs a 150 amp but the wire is only rated for 100 amps, that's a problem.

Rafe

Cat Daddy said:

One more thing to consider. The breaker also protects the wire and needs to be sized accordingly. If the winch needs a 150 amp but the wire is only rated for 100 amps, that's a problem.

Rafe

Click to expand...

Yes, good reminder

You have to get into some high theory to guess the results of breakers in parallel but it is not going to yield the sum of two ratings.

Jim,
What was the thought for the DC1200? I believe the KK42 was engineered around a 500# lift for mast/boom rigging and stability. Just curious because I am currently installing DC800 on my KK42.

Scott

Scott: Good point. I'm not certain. I have a KK42 and my skiff is probably only 350 lbs, max. I will contact S3 before I proceed. They came to our "Krogin" in Anacortes. They do all the commissioning for new KK's on the west coast. They probably recommended the Warn 1200 because that's what they put on for the new builds, which are typically bigger vessels than mine.

Jim

bayview said:

You have to get into some high theory to guess the results of breakers in parallel but it is not going to yield the sum of two ratings.

Click to expand...

After researching several electrical engineering websites/forums...

Seems that....

1. Parallel fusing in the US is not allowed for circuit protection but OK in devices.

2. Parallel fusing is fairly common in some devices and works great if the fuses are the same size.

3. Using different sized fused can result in all kinds of tripping sequences...but as long as the largest fuse is smaller than the ampacity of the wire... and the combined total is smaller also...there isn't a lot "danger" involved that a quick read showed.

So I guess if the setup has been working so far...other than following standards it seems to be a crapshoot.


Parallel fusing with equal fuses CBs doesn't seem complicated but there are efficiency issues that need to be addressed and what appears to be another constant or so if you really want perfection. Not the same size...well...it's rarely discussed.

We use series breakers in a nuclear power plant for motor loads that penetrate primary containment. One breaker is setup specifically to protect the motor. Because its a motor, there are design conditions that must be met and verified through periodic testing. The other breaker is sized specifically to prevent damage to the primary containment penetration and has completely different design and testing requirements. Neither breaker alone can meet both sets of requirements and both must operate independantly. Other than that, I can honestly say that in 40+ years in the electrical field, I've never seen 2 breakers used for one load that werent mechanically ganged together to trip at the same time until this post. Me thinks the installer was more of a mechanical guy.

While I have never done it, it would seem to me that with a 50 and a 100 amp breaker, both would trip around 110 amps. With parallel circuits of equal wire gauge size, the current would flow equally over each conductor (path of least resistance). When the 50 amp breaker saw 55 amps +/-, it would trip sheading its load to the 100 amp breaker which would now trip with a 110 amp load.

Ted

Our Warn DC1200 hoist lists max draw at 100 amps and 1200 lbf. It is part of a davit system, not the factory boom and mast from Krogen. Does your lifting system have 2 winches?

Per NEC 240.8: "Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel."

Yes Larry, it has two winches. I only operate one at a time. These are the "Rule" winches.


Jim
Sent from my iPad using Trawler Forum

High Wire said:

We use series breakers in a nuclear power plant for motor loads that penetrate primary containment. One breaker is setup specifically to protect the motor. Because its a motor, there are design conditions that must be met and verified through periodic testing. The other breaker is sized specifically to prevent damage to the primary containment penetration and has completely different design and testing requirements. Neither breaker alone can meet both sets of requirements and both must operate independantly. Other than that, I can honestly say that in 40+ years in the electrical field, I've never seen 2 breakers used for one load that werent mechanically ganged together to trip at the same time until this post. Me thinks the installer was more of a mechanical guy.

Click to expand...

Wow! Archie you sure brought back memories of an earlier life for me....countless hours sitting in front of an old SR76 or EPOCH test set shooting penetration breakers during refueling outages! Nice to know there are a few old power nukes still afloat.
Back OP's subject...I agree this was probably something configured by a "boatyard electrical expert", and lacks basis in both theory and application....Replace the two breakers with one that is properly sized for the load.

Thanks all! I will go ahead and replace that breaker combination, but will wait until I replace the winches as the new ones may have a different requirement. They won't be used much in the next few months anyways.

The setup seemed odd, even for this electrical lightweight!

Jim

>Thanks all! I will go ahead and replace that breaker combination, but will wait until I replace the winches as the new ones may have a different requirement.<

The CB are usually sized to protect the wiring , not the user.

A slow blow fuse works best for that.