Mcb problem

[SamKingfisher]

So, following advice on here, I have run my solar "backwards" through a 30a mcb in the fuse box, previously it was a 30a blade fuse before the batteries.

 

I have confirmed with Google that MCBs should work in both directions.

 

I'm not seeing more than 12a from the array, yet the mcb is tripping.

 

Bigger mcb, or sack it off for a midi fuse? Or..

 

Faulty mcb? They don't like it backwards?

[by'eck]

So, following advice on here, I have run my solar "backwards" through a 30a mcb in the fuse box, previously it was a 30a blade fuse before the batteries.

 

I have confirmed with Google that MCBs should work in both directions.

 

I'm not seeing more than 12a from the array, yet the mcb is tripping.

 

Bigger mcb, or sack it off for a midi fuse? Or..

 

Faulty mcb? They don't like it backwards?

 

MCB's are for protecting mains AC distribution circuits with a variety of trip profiles.

 

No reason they wouldn't work with low voltage DC I suppose but likely the trip current rating will differ, which may explain your issue.

[SamKingfisher]

Loads of people use them with 12v.

[by'eck]

Loads of people use them with 12v.

 

Lots of people do lots of daft things but that doesn't make it right. You may find by digging deep in the spec a DC current rating for your AC MCB though. As I've said chances are it will be different to the design AC trip current rating.

 

You asked for an explanation of your issue, this may well be it.

[5thHorseman]

misunderstood your post

Edited October 12, 2014 by 5thHorseman

[SamKingfisher]

I should explain that the boat was built by Debbies Day Boats with a bank of MCBs in a consumer unit for the 12v. This has worked perfectly for 11 years. Only this latest addition is giving trouble.

[SamKingfisher]

http://destinynarrowboat.weebly.com/12v-dc-system.html

[SamKingfisher]

http://www.hagerelectro.com.au/downloads-services-support/faq/84.htm

[Paul C]

I should explain that the boat was built by Debbies Day Boats with a bank of MCBs in a consumer unit for the 12v. This has worked perfectly for 11 years. Only this latest addition is giving trouble.

 

Shouldn't have passed BSS like this - our boat (before we bought it) had this arrangement, was surveyed (which also included a BSS test) and this was picked up as a "fail" item - so it was replaced with a more conventional 12V fusebox and breakers by the seller.

From post #8's link:

 

 

 

Can I connect a Hager RCD to a DC supply?

No. Hager RCCBs and RCBOs are not suitable to be connected to a d.c. supply.

[Paul C]

PS Just had another look at the first link (in post #7). Two points to note:

 

1) Its completely meaningless to use as an authoritative source - its someone's blog of their DIY build by the looks of it.

2) The advice they give seems to contradict the "official line" given by the Hager FAQ link supplied - either he was given bad advice; their FAQ is overly cautious; he has a slightly different product in his consumer unit than the MCB's the FAQ relates to, or he's simply got it wrong. I suspect he was given poor advice or misunderstood something along the way and convinced himself it was okay.

Edited October 13, 2014 by Paul C

[by'eck]

I guess from a lazy builders point of view being able to use one of those large consumer units with shed loads of MCB's mounted on a DIN rail makes for an easy installation. Hager MCB's aren't that cheap though and money/space saved by using combined circuit breaker switches dedicated to DC such as these Carling switch ones which come in a variety of current ratings up to 25 amps, and fitted to a home made panel. No BSS issues either though it could be argued that use of MCB's are not grounds for a fail.

 

Edited October 13, 2014 by by'eck

[John V]

 

Shouldn't have passed BSS like this - our boat (before we bought it) had this arrangement, was surveyed (which also included a BSS test) and this was picked up as a "fail" item - so it was replaced with a more conventional 12V fusebox and breakers by the seller.

From post #8's link:

 

 

 

He is not using RCCB's or RCD's he is using MCB's......totally different animals and MCB's of most makes are fine for DC use , instead of using "B's" or "C's" use "A" curve MCB's as these will trip closer to the rated figure.....Any BSS inspector who says they are no good is talking out of his A....

[ditchcrawler]

No BSS issues either though it could be argued that use of MCB's are not grounds for a fail.

 

 

I agree with that. I am not anti BSS I just feel that sometime people get failures when in fact they comply.

[raymondh]

Most if not all Aqualine boats use MCB's as standard so as stated any BSS "inspector" who suggests they are a fail is talking out of his/her A&se

 

Ray

[Tony Brooks]

 

 

He is not using RCCB's or RCD's he is using MCB's......totally different animals and MCB's of most makes are fine for DC use , instead of using "B's" or "C's" use "A" curve MCB's as these will trip closer to the rated figure.....Any BSS inspector who says they are no good is talking out of his A....

 

 

Yes, but are the contacts DC rated or fitted with suitable arc suppression for DC use? They will break at least once but they could then well be burning or welding their contacts if only AC rated.

[Ryeland]

Having used MCBs professionally on 48V DC systems, I know that very few manufacturers give a DC rating. ABB are one whose products I have used. On my boat I haven't bothered - if one burns it's contacts on breaking a fault I'll replace it. I suppose they could weld when reset after a fault after they burn but IMHO this is very unlikely. More likely they will not make a good enough contact to be used, prompting replacement.

 

Richard

[SamKingfisher]

From Hager faq.

 

"Can I use a hager MCB to protect a DC system?

Yes, maximum voltage is 60Vd.c. using 1 pole or 125Vd.c. using 2 poles. The breaking capacity of the MCB remains the same although the magnetic tripping point is increased by 50% (i.e. a C-curve characteristic is altered from 5 - 10 x In to 7.5 - 15 x In)"

 

Please don't comment on electrical installation threads if you don't know what you are on about.

[Guest]

 

Lots of people do lots of daft things but that doesn't make it right. You may find by digging deep in the spec a DC current rating for your AC MCB though. As I've said chances are it will be different to the design AC trip current rating.

 

You asked for an explanation of your issue, this may well be it.

You could well be right. Some are fine at 12Vdc, some aren't. I used Hager ones which were approved at 12V dc by the manufacturer at the time of fitting. MK ones definitely were not suitable (at that time.) I have forgotten which other ones were OK.

I guess from a lazy builders point of view being able to use one of those large consumer units with shed loads of MCB's mounted on a DIN rail makes for an easy installation. Hager MCB's aren't that cheap though and money/space saved by using combined circuit breaker switches dedicated to DC such as these Carling switch ones which come in a variety of current ratings up to 25 amps, and fitted to a home made panel. No BSS issues either though it could be argued that use of MCB's are not grounds for a fail.

 

I talked to the boat safety inspector re this subject, who is also an electrician. He preferred suitable 240V style mcb's. That is just one inspector of course, others will have different views.

[nicknorman]

Thank god we don't have individual fuses in the distribution system. Far too much clunky electromechanical hassle!

[Guest]

Thank god we don't have individual fuses in the distribution system. Far too much clunky electromechanical hassle!

Me too, fuses went out with the ark. However breakers are a different matter.

[by'eck]

You could well be right. Some are fine at 12Vdc, some aren't. I used Hager ones which were approved at 12V dc by the manufacturer at the time of fitting. MK ones definitely were not suitable (at that time.) I have forgotten which other ones were OK.

I talked to the boat safety inspector re this subject, who is also an electrician. He preferred suitable 240V style mcb's. That is just one inspector of course, others will have different views.

 

I wonder what the grounds for his preference were.

 

BTW although Hager suggest they can protect DC circuits, the limit is 60 volts and they also point out that the magnetic trip point can increase by 50%.

 

Apart from not being used for design purpose, the extra cost and bulk etc., I'm also concerned given the stiff spring action, how well they cope with everyday switching use.

Edited October 13, 2014 by by'eck

[nicknorman]

Me too, fuses went out with the ark. However breakers are a different matter.

Ok maybe I should have said "individual breakers" - as I said, electromechanical clunkery. No moving parts for us.

[John V]

 

 

Yes, but are the contacts DC rated or fitted with suitable arc suppression for DC use? They will break at least once but they could then well be burning or welding their contacts if only AC rated.

 

 

 

This is not an exhaustive list but these makes of mcb are rated for DC Schneider (Merlin Gerin), ABB, Hagar, Kopp, Lovato, and Moeler GE and Crabtree were but I do not have up to date spec sheets to check

[by'eck]

 

 

Yes, but are the contacts DC rated or fitted with suitable arc suppression for DC use? They will break at least once but they could then well be burning or welding their contacts if only AC rated.

 

Good point although as mentioned if you delve deep in the spec most have a DC rating.

 

Came across an interesting fact regarding DC breaker spark suppression. Without modern switch design the arc created when DC contacts are opened to reduce current to zero is approx 1mm in length per volt. This means that a traction system breaker operating on 750 volts DC could develop an arc 30 inches long!

[Guest]

 

I wonder what the grounds for his preference were.

 

BTW although Hager suggest they can protect DC circuits, the limit is 60 volts and they also point out that the magnetic trip point can increase by 50%.

 

Apart from not being used for design purpose, the extra cost and bulk etc., I'm also concerned given the stiff spring action, how well they cope with everyday switching use.

I don't use mine as switches, so can't comment.

I seem to recall that the surveyor felt that some dedicated boat electrical stuff was rather "Mickey Mouse."

I was informed by Hager that 60V DC is the upper limit?

 

I have said this many times on here over the years, but once more:

I picked up a panel in a chandlers once which was marketed for 12Vdc on narrowboats, which had separate switches and breakers. It looked very good and fit for purpose, so good I nearly bought one. Until I looked closely at the back of the switches, which were marked "for 240V AC only!"

 

I went with generic breakers after that, though did consider HRC fuse links.

Ok maybe I should have said "individual breakers" - as I said, electromechanical clunkery. No moving parts for us.

I was being mischievous, I knew what you meant really

 

 

This is not an exhaustive list but these makes of mcb are rated for DC Schneider (Merlin Gerin), ABB, Hagar, Kopp, Lovato, and Moeler GE and Crabtree were but I do not have up to date spec sheets to check

I definitely remember Crabtree being approved, but it was ten years ago!