Hello from Scotland - with a question on circuit breakers/fuses

[tgm]

Hello all - I have just joined this community - the sun is shining and the amps are flowing in. I have a question for you all. I have a 48 volt hybrid wind and solar system and am looking for a 30 amp fuse or circuit breaker. Can I use a 30 amp 32 volt fuse safely or a 30 amp 120/240 circuit breaker safely and if not does anyone know where I can get hold of some here in the UK?

[inetdog]

Hello tgm, and welcome to Solar Panel Talk!

Under no circumstances use a fuse rated lower than 50V DC or a circuit breaker not rated for DC.
They will not be able to extinguish the arc resulting from breaking the 48+V DC circuit and the eventual result will be self-destruction or a fire.

You can get higher voltage DC fuses from some marine supply outlets. Blue Sea is a reputable fuse manufacturer sold here in the US.
You can also order over the internet from Solar Town, one of the sponsors of this forum (see link on main page.)
The main supplier of DC circuit breakers that will serve the purpose well is Midnite Solar, but you may also be able to buy directly from the manufacturer they use.
Be careful since some DC circuit breakers are polarized and will only properly interrupt current flowing in one direction through the breaker.

[SunEagle]

Hello all - I have just joined this community - the sun is shining and the amps are flowing in. I have a question for you all. I have a 48 volt hybrid wind and solar system and am looking for a 30 amp fuse or circuit breaker. Can I use a 30 amp 32 volt fuse safely or a 30 amp 120/240 circuit breaker safely and if not does anyone know where I can get hold of some here in the UK?

My question would be, what is the voltage of the circuit you want to install that 30amp fuse?

You mentioned a 48v (presume that is DC) and 120/240v (presume that is AC) so that 32volt fuse will not work in either of those voltage circuits.

[Raul]

That's a easy one , for 240v 32a you can get a Mcb from your local wickes, b&q , screwfix, toolstation , TLC direct for about £6.
If you looking for some DC aplications look for Schneider, sqareD rated for dc&ac , you can get lots on eBay posted to your door or your local electrical shop .

[tgm]

Hello tgm, and welcome to Solar Panel Talk!

Under no circumstances use a fuse rated lower than 50V DC or a circuit breaker not rated for DC.
They will not be able to extinguish the arc resulting from breaking the 48+V DC circuit and the eventual result will be self-destruction or a fire.

You can get higher voltage DC fuses from some marine supply outlets. Blue Sea is a reputable fuse manufacturer sold here in the US.
You can also order over the internet from Solar Town, one of the sponsors of this forum (see link on main page.)
The main supplier of DC circuit breakers that will serve the purpose well is Midnite Solar, but you may also be able to buy directly from the manufacturer they use.
Be careful since some DC circuit breakers are polarized and will only properly interrupt current flowing in one direction through the breaker.

Thanks for your quick reply. I have had a real rpoblme in getting 48 Volt fuses ect over here and had been using a 6.6 amp/240 volt circuit breaker for the wind turbine which requires a 30 Amp 48 Volt fuse/circuit breaker. My knowledge of electrics is very limited so I have been relying on following manufaturer instructions and school physics of watts = Amps x Voltage AC or DC was unknown to me exept in terms of 'behviour' ie DC one-way AC forward and back. I think I have been lucky then for the last while as I have not had a DC breaker.. or indeed a fire! I had suspected that this might be a problem (thus this query) and have been uneasy about it since I set it up.

I am off grid and have a small system with 4 x 120 watt 12 volt panels in series. My wind system comprises a futurenergy 1kw turbine with switch, have a chinese solar controller and a xantrex c40 charge controller, a victron phoenix 750a inverter, 2 dump loads, 4 x Rolls 5000 Series 12CS11 12vbatteries and used 10mm Tri Rated Cable throughout. I did get the system checked by an electrician but I have always been concerned about the fuses.

House side is okay as the victron is even more sensitive than the consumer unit - but battery side this has always worried me. Periodically I have looked for 30 amp 48 volt fuses/circuit breaker but they never seem to turn up. As a novice (but learning) all your responses have been appreciated.

I am obviously not very clued up on this but as a general point can you let me know if and why a similar rated fuse or circuit breaker would perform differently if AC or DC?

[tgm]

[QUOTE=SunEagle;179465]My question would be, what is the voltage of the circuit you want to install that 30amp fuse?

You mentioned a 48v (presume that is DC) and 120/240v (presume that is AC) so that 32volt fuse will not work in either of those voltage circuits.[/Q

Yes SunEagle you are right I was referring to 48 volt DC for the solar/wind and 120/240 for the circuit breakers as they were they only ones I could find apart from the 30 amp 32 volt Dc fuse. Was wondering if 50 would be better for the latter. The main reason I asj=ked the question is that I cannot find the correct fuse but I had been told by another wind person that 30 amps at any rating would be okay - that just doesn't seem right to me.

[Raul]

Schneider electrics does DC-AC circuit brakers . If you ask your local electrical shop will order it in for you. That's what I did. Or look on eBay they pop up as 3pole for 415v AC- 250v DC .
Another make is IMO used currently very much on solar instals . There is one on eBay now on 40 with best offer . New Eaton 30a 250v dc double pole.

[inetdog]

I am obviously not very clued up on this but as a general point can you let me know if and why a similar rated fuse or circuit breaker would perform differently if AC or DC?

Sure. One of the characteristics of the back and forth nature of the current in an AC circuit is that each time it reverses direction the current has to pass briefly through zero.
And an electric arc is kept going by the electrons (and ions) moving through the electric field hit air molecules and ionize them. The result it lots of electrons and ions to carry the current. During the time the current is zero the ions all get together and form neutral air (nitrogen, oxygen, etc.) molecules. When the voltage builds up again in the other direction the gap between the contacts is now large enough that the arc cannot restrike and start up again. (Like with an arc welder you have to get the electrode very close to the workpiece (momentarily touching) to get the arc started, but then as long as the current stays continuous you can pull the electrode farther away. Once the arc extinguishes you have to go in close again to restrike it. )

With DC the current will not, by itself, go through zero. So you have to stretch the arc out, block its path, cool it, move the contacts very far apart and in general do something active to interrupt the arc.
In an AC switch or breaker (or even fuse) the DC arc may continue indefinitely, heating and eating away at things around it the whole time.

[Living Large]

I am obviously not very clued up on this but as a general point can you let me know if and why a similar rated fuse or circuit breaker would perform differently if AC or DC?

Interesting factoid. DC power service lasted into the 1960's in parts of Boston, including the hotel where Tesla (AC pioneer) died in the 1940's.

[tgm]

Thanks inetdog for that explanation - very clear and easy to understand. Thanks also Raul - have done as you suggest just waiting on them getting back to me.