rear power sockets

Submitted: Friday, Apr 30, 2004 at 07:35

ThreadID: 12498 Views:2008 Replies:5 FollowUps:13

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craig

Hi all just wanted to ask a few questions about putting in some rear power sockets in my rangie.
I have done a search and it seems that 6mm wire is the go for this but this might be a stuppid question but is 6mm the thickness of a twin core wire or is it 6mm for both the + and the - wire ?
Also what size fuse do most people run ? the socket will be for running a fridge and lights and one for a shower pump.
Also It seems alot of people use the hella plug, can anyone suggest a mail order place to get plugs as I cant seem to fing any here in the UK.

Thanks for any info.

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Reply By: Ian Bee - Friday, Apr 30, 2004 at 07:50

Reply By: Rosscoe - Friday, Apr 30, 2004 at 08:52

Friday, Apr 30, 2004 at 08:52

IMO 6 mm wire is minimum and one must be aware that there are several methods of sizing wire. BS, AWG, Auto to name a few.
Bottom line is the overall size of the conductor NOT the overall size of the wire and insulation is what you must be concerned with. The larger the conductor the lower the resistance and therefore less voltage drop which is your ultimate goal.
So ,again IMO, you should use a minimum of 6 mm square cross sectional area (6 mm wire you buy from an auto shop is only about 4 mm square although a lot people use this and seem happy)
Cross sectional area is equal to Pi x radius of the the conductor squared.
Best to use 6mm square wire for both positive and negative and wire the negative all the way back to the engine or suitable earth return point not just the car body at the rear of the vehicle.
Suggest you use an automatic ciruit breaker (say 20 A) as close as practical to the battery poisitive and a 10 A fuse for the appliances. Theoretically the CB protects the cable, the fuse the appliance. The fuse should therefore be close to the appliance. An in-line fuse is a possibility.
Can't help with a supplier of Hella connectors but agree they are far better than the standard cigarette lighter type. Try the Hella web site for UK distributors.
Alternative is to use the connector supplied by the fridge manufacture eg Engel make one with a long loom and one with a short length of cable including 10A in line fuses.

AnswerID: 56672

Follow Up By: Cruisergxl - Friday, Apr 30, 2004 at 10:05

Friday, Apr 30, 2004 at 10:05

If you check some of the posts on the forum a while back there is some good info on plugs and sockets. Try PostID: 12167

FollowupID: 318421

Follow Up By: Dion - Friday, Apr 30, 2004 at 10:29

Friday, Apr 30, 2004 at 10:29

Rosscoe, a fuse is not fitted to protect the appliance. Protection devices, doesn't matter wether it is a fuse or circuit breaker is fitted to protect the wiring and to a limited degree the source of power. Manufactureres of appliances install fuses or circuit breakers within the appliance itself it is a quality product.
Each manufacturer of wire specifies the maximum continuos current rating of the wire. One manufacturer of 6mm2 may say his wire is rated at 16Amps where as another may say his 6mm2 wire will carry 20Amps, importantly you shouldn't add some fat to the fuse or circuit breaker rating. The fuse or circuit breaker rating should never exceed the rating of the conductors used. You are better off 'over engineering' the conductors and increasing the size of the conductors and then an appropriate size fuse.
Yes the protection device for the conductors should be as close as possible to the source of the power, within about the first 200mm from the battery in this case.

Cheers,

Dion.

FollowupID: 318422

Follow Up By: Rosscoe - Friday, Apr 30, 2004 at 10:49

Friday, Apr 30, 2004 at 10:49

Dion,
There are many ways to skin the proverbial cat!
The continuous current rating of the cable has more, if not all, to do with the insulation material/ thickness etc. and its temperature limits. Provided there are not high resistance connections, P = IR squared. If the cable resistance is low there will be little heat developed in the wire.
Hence a CB can be rated for the cable but the fuse for the appliance.

FollowupID: 318424

Follow Up By: Dion - Friday, Apr 30, 2004 at 11:46

Friday, Apr 30, 2004 at 11:46

Rosscoe,
The continous current rating is as applicable to the conductor, and only to a lesser extent, the insulation. A manufacturer will fuse an appliance if necessary, there is no need for a fuse to be added by the user to protect an appliance. How can a fuse added by a user in the conductors to an appliance protect the appliance? Some fuses in appliances are to protect from reverse polarity, others are where there are several subcomponents in an appliance.
The fuse or circuit breaker that an user adds to be conductors, in the context we have here, for an accessory plug in a 4by is to protect the conductors from creating heat in a short circuit situation, where the conductors could create so much heat the insulation (no matter how thick) will spontaneously combust - I've seen it happen, not pretty.
There is a seperate classification for insulations applied to conductors.
Conductors, bigger is still better.

Cheers,

Dion.

FollowupID: 318441

Follow Up By: Dion - Sunday, May 02, 2004 at 13:30

Sunday, May 02, 2004 at 13:30

Rosscoe,
not sure where you derived the formula P = IR squared from in your 30 April 10:49 post. I use the following four formula's and I just could not transpose any of them to get P = IR squared.

V = IR

P = IV

V(squared) = PR

P = I(squared)R

It is important to use the 'square' function in the correct place, and square only the current, not the product of current and resistance.

Cheers,

Dion.