[jim bean]

Was just about to install a split charge relay to my system when I realised I only have a 30a online fuse use? Leisure battery is 70ah,
Will this Be sufficient or should I get a 70a fuse?
Thanks

[Susan Dean (1stclean)]

thats fine , the fuse is there to blow if anything starts to fail and not wait until the last minute

[jim bean]

Thanks very much 

[duncan h]

the 30amp is what its drawing from, ie pump. Same as house fuses.

[Simon Trapani]

I think the 30 amp is the maximum charge rate actually so it will be fine. The pumps & controllers themselves just need a 7.5 amp fuse.

Spruce  or Ian Sheppard will be along  soon I'm sure to confirm.

[Don Kee]

Firstly you should have two inline fuses for your split charge relay (I'm going on the assumption its an intelligent relay)

One between van battery and relay, and one between relay and leisure battery (have the fuses as close to batteries as possible)

The 30amp fuse you've been provided should be fine. The inline fuses you have should be in accordance to the max out put of your split charger (nothing to do with pump draw, battery size etc...)
So if you have a 30amp relay, the a 30amp fuse should be fine
(On a side note, the 30amp means you charge 30amps per hour, so if you have a 70ah battery it'd take just over 2 hours of your van being on to charge the leisure battery in theory)

As susie has said, the fuses are there in case of a power spike or failure, the fuse blows first so not to blow your relay and wiring (hence why you put the fuse as close to the batteries as possible)

[Spruce]

No good putting in a 30 amp fuse if your wiring will only carry a current of 20amp. Your fuse must be your 'weakest link'. So if you have 20 amp cable the max fuse amperage would be 15 amps.

[Don Kee]

No good putting in a 30 amp fuse if your wiring will only carry a current of 20amp.

Good point