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[Warthog]

See, i knew a grown up would come along

Buggered if i could find those conversion though

[Nexus]

Lornaben,
I know that conversion, but am not sure that it can be directly applied to a contact rating, if you look at a relay for example at 250v Ac at 10amp it is only usually rated at 125vac 15 amps so their is not a direct scaling of the figures.  But I am buggered if I can find a website that easily explains it.  The contact rating is based around the amount of amperage that the contact can take before it rises 30/40 degrees c over the ambient conditons at the contact area I believe in which case it is very unlikely that the contact area can sink 500 amps.  I will do some more searching though as an interim I will get the switch anyway.

Cheers
Nick

[Lornaben]

Your quite right Nick, theory and practice don't equate to the same thing.

The 250 Amp rating will be the minimum test rating, so 300 would be a reasonable assumption. Dropping the voltage will increase the Amperage but as you say not directly twice. Using that ideal, 500 Amps wouldn't be an unreasonable expectation at 12 Volts either. Don't forget it will sink 2500 Amps @ 24V albeit for a short period.

Don't loose sight of the fact its all a guide though, after all we're not talking precision electronics.  

[Nexus]

Thanks, for the input its been a good discussion, have ordered the isolator + other bits, will be ordering the winch tomorrow morning.  So may be able to electrocute myself on the weekend
to be safe I will probably stand in a bucket of water whilst clutching a lightening conductor, whilst balancing on one leg  

Cheers
Nick

[Lornaben]

Did a bit more research, the load ratings are tested at 125% of listed rating. So at 24 Volts it will comfortably take 312 Amps.

I've even emailed Durite for a definitive answer for 12 Volts.

[Lornaben]

Just realised they never replied, I'll be givin em a ring tomorrow 

[Nexus]

Already fitted a 250 amp one to the front of the jeep, stressful drilling holes in the body work though technically it's lightened the jeep until I bolted all the other crap on 

Cheers
Nick

[Lornaben]

OK, I had a reply email from Durite. They sent me their standard spec sheet for the isolator  

I gave them ring and had chat with one of their technical geezer's ...

ME - What constant amperage will it take @12V ?
Geezer - 250 ....
ME - OK, I thought that was at 24V ?
Geezer - The defined spec is 250 Amps max at a max 24V ....

After a conversation about the conversions I posted earlier in the thread, Nick is right on the mark when it comes to converting ratings. You cant use them to estimate ratings based on different voltages. I decided to ask a few searching questions based on the 'defined spec' stating 2500 Amps for 5 seconds
He stated a few specs based on my questions but wouldn't put them in writing 'because it hasn't been bench-marked to define a controlled specification' (or very similar words)

These are the guidelines to what the isolator will take (in his qualified opinion, but not Durites) He also stated that these would all be with the isolator fully engaged before any load is put through it. If you try to use it as a switch the contacts will be damaged by arcing occurring as the contact engages and disengages.....

300 Amps - some considerable time, probably constantly.
400 Amps - At least 20 mins or so with a rest of about 20 minutes.
500 Amps - 10 - 15 mins or so with 20 mins to cool.
600 Amps - Several minutes with 20 mins to cool.
700 Amps - A few minutes at most
800 Amps - maybe a minute ..

So there we have it, not as good as I was led to believe by LSUK but still up to the job.

Interestingly, he said the lighter duty isolator is not really up to the job of isolating a winch ...