AC vs DC Thermal Magnetic circuit breaker

[Delfini]

I have just bought a Lewmar Electric winch conversion kit and looking at the electrical requirements - the kit is supplied with a panel mounted 80A thermal DC breaker but my 24v distribution panel has a number of DIN rail mounted 80A breakers and I would prefer to use this set up for protecting the winch motor - the breakers already fitted and protecting the inverter, the windlass, the water maker and the battery charger are from E-T-A and marked 410-K-2-02

That part number denotes a single pole high performance thermal-magnetic circuit breakers for AC 240/3 AC 415 V/3 AC 500 V or DC 110 V

Im not sure if I can still buy these breakers but if I can’t is there a critical part of the spec I should look for in an equivalent - Ive read elsewhere you can’t use AC breakers in a DC environment but this clearly isn’t true for E-T-A

Thanks

 

[Boater Sam]

Merlin Geran, now Schneider, MCBs are approved for DC and are din rail mounted

 

[JumbleDuck]

Im not sure if I can still buy these breakers but if I can’t is there a critical part of the spec I should look for in an equivalent - Ive read elsewhere you can’t use AC breakers in a DC environment but this clearly isn’t true for E-T-A

Most things with breaking contacts (switches, relays, breakers) have lower DC ratings that AC. That's because at 50Hz the arc which forms breaks after at most 1/100s (next time current goes through zero) and doesn't re-establish whereas the DC arc lasts much longer and does more damage to the contacts.

As far as I can see, you should be fine with a 410-K-2-02-SI-80A although the SI may have a significance I haven't spotted. That's good for 80A at 110V DC. Costs £230 + VAT or so.

 

[Delfini]

Most things with breaking contacts (switches, relays, breakers) have lower DC ratings that AC. That's because at 50Hz the arc which forms breaks after at most 1/100s (next time current goes through zero) and doesn't re-establish whereas the DC arc lasts much longer and does more damage to the contacts.

As far as I can see, you should be fine with a 410-K-2-02-SI-80A although the SI may have a significance I haven't spotted. That's good for 80A at 110V DC. Costs £230 + VAT or so.

Thanks - I don’t know what I think about paying £230 for a DIN mounted breaker when I already have a panel mounted version but Im not totally comitted

 

[TSB240]

I have been building electrical control panels using standard din rail mounted miniture circuit breakers for 24v DC circuits for many years.
You should be able to source an IMO breaker at a tenth of that price. They are rated at up to 60v DC.

 

[noelex]

Most (but not quite all) DIN rail MCB are rated up to a reasonable DC voltage (around 48+V DC). They are, in most ways, superior to “marine” circuit breakers. The greatest advantage is that they are very easy to change if a fault develops (circuit breakers switching DC can fail after a reasonable number of operations). Many manufacturers produce near identical products so a replacement is always readily available.

The exception is electric propulsion and high voltage solar panels. These high voltage applications can occasionally require specialised DC breakers on boats. DIN rail versions of these high voltage breakers are readily available, but high quality, high voltage, “name brand” DIN rail circuit breakers are expensive, especially above 60v. However, there are no “marine” equivalents. There are also many quite inexpensive “no name” high voltage DC DIN rail breakers that seem to work well despite the low price.

In short, DIN rail MCB are a great alternative and will generally be an excellent choice with marine DC voltages.

 

[jackho]

I have just bought a Lewmar Electric winch conversion kit and looking at the electrical requirements - the kit is supplied with a panel mounted 80A thermal DC breaker but my 24v distribution panel has a number of DIN rail mounted 80A breakers and I would prefer to use this set up for protecting the winch motor - the breakers already fitted and protecting the inverter, the windlass, the water maker and the battery charger are from E-T-A and marked 410-K-2-02

That part number denotes a single pole high performance thermal-magnetic circuit breakers for AC 240/3 AC 415 V/3 AC 500 V or DC 110 V

Im not sure if I can still buy these breakers but if I can’t is there a critical part of the spec I should look for in an equivalent - Ive read elsewhere you can’t use AC breakers in a DC environment but this clearly isn’t true for E-T-A

Thanks

I cant imagine a MCB switching an 80A DC load. Maybe a very specialized and costly item. In my case the MCB only supplies the feed to the relay which energizes the say 80A contactor. Same to for the anchor winch.
I have recently fitted an electric winch and preferred to use the supplied breaker connected to the service battery via. new isolator switch (and inline fuse).

 

[noelex]

I cant imagine a MCB switching an 80A DC load. Maybe a very specialized and costly item. In my case the MCB only supplies the feed to the relay which energizes the say 80A contactor. Same to for the anchor winch.
I have recently fitted an electric winch and preferred to use the supplied breaker connected to the service battery via. new isolator switch (and inline fuse).

80A DC MCB are possible at marine voltages even without resorting to a specialised DC breaker. This is one example:

A9N18341 - Miniature circuit-breaker, Acti9 C120N, 1P, 80 A, B curve, 10000 A (IEC 60898-1), 10 kA (IEC 60947-2) | Schneider Electric Global

 

[noelex]

I cant imagine a MCB switching an 80A DC load. Maybe a very specialized and costly item. In my case the MCB only supplies the feed to the relay which energizes the say 80A contactor. Same to for the anchor winch.

The 80A contactor will switch the load, but you still need circuit protection.

Using a circuit breaker to supply a feed for a relay will only protect the small current in the coil circuit, but protection for the primary high current is still needed.

 

[Delfini]

Thanks all - as “noelex" said, the Lewmar controller/contactor provides the switching function and thermal protection for the motor and the 80A breaker is primarily there to protect the wiring under fault conditions - in the end I found out that E-T-A are still operating in the UK and the item I was looking for is available to order for less than £100 - so that’s what I went for

 

[jackho]

The 80A contactor will switch the load, but you still need circuit protection.

Using a circuit breaker to supply a feed for a relay will only protect the small current in the coil circuit, but protection for the primary high current is still needed.

yes that is why I fitted the 80a inline fuse. I guess the difference is he fitted the hi amp MCB whereas I used the provided overload device close to the motor and connected direct to battery via isolator sw. to minimize cable run and subsequent volt drop. (I should imagine adding an additional 80a load onto an existing "bus train" with additional MCB would require an upgrade to supply wiring - not to mention the cable sizes involved.) I couldn't imagine running i think 16sg cable anywhere near my Dist. panel to supply winch but realize his may be a different setup.

 

[noelex]

yes that is why I fitted the 80a inline fuse. I guess the difference is he fitted the hi amp MCB whereas I used the provided overload device close to the motor and connected direct to battery via isolator sw.

Rather than close to the motor, the circuit protection device (fuse or circuit breaker) is ideally located as close to the batteries as is feasible.

to minimize cable run and subsequent volt drop. (I should imagine adding an additional 80a load onto an existing "bus train" with additional MCB would require an upgrade to supply wiring - not to mention the cable sizes involved.) I couldn't imagine running i think 16sg cable anywhere near my Dist. panel to supply winch but realize his may be a different setup.

Unless the distribution panel is in a suitable location, normally for a high powered device such as an anchor winch, the MCB would be located in seperate sub panel to minimise the wire run. It is often not ideal to mount all the circuit breakers in one location especially on a larger vessel. For example, in your installation the isolating switch could be replaced with a circuit breaker eliminating the extra connections that you have with a fuse. The curcuit breaker would also provide easier and quicker resetting ability.

One nice aspect of DIN rail mcb is that there is plenty of suitable mounting boxes available, which makes installing a sub panel simpler. Surface mounted marine circuit breakers such as the BlueSea 187 series are also quite good and easy to install, although they are only thermal circuit breakers and have a reasonably low IC current.