will amp wirin fail nct??

[_bmw_316_lad_]

hi lads a mate told me that if you have a amp wired up thhat it fails the nct due to it bein a fire hazard?? is this truedoes any 1 no???

[Alex]

whats nct

[mrLEE30]

it depends on how you wire it in. If you take power from the battery directly then out of good prctice and safety you should put an inline fuse AS CLOSE TO THE POSITIVE TERMINAL AS POSSIBLE this way the fuse protects against and problems with the wire. the size of the fuse depends on what amp you have, but most amps have a built in fuse, so your inline fuse couls be the same rating.

if the unit is fused properly then it cannot be a fire hazard.

mrlee

[_bmw_316_lad_]

its the irish version of the mot. thanks mrlee its wired proper alright

[maxfield]

Does it even make a difference being wired close to the battery terminals?

[mrLEE30]

yes max it makes a huge difference, as i keep bangin on about!

a DC battery is a very powerful device able to generate large amounts of power at 12 volts and as you will remember from pyhsiscs power is volts times amps. under a short circuit condition there is little resistance (or no) between the + and - of the two terminals, and again the old V=IR where we have a fixed V (12V) a very low R thus a very high I or current.

now lets think about this as your stereo wiring, you run you nice big cable from the battery to you amp, and assuming the bat is in the front you run your wire to the amp in the boot, this wire passes through various metal parts, under the carpet etc etc, so if there is a break in the wire insulation (due to rubbing, or poor installation) then it could touch the chassis and thuerefore the battery negative, thus a short circuit, loads of power round this cable, which generates tremendous amounts of heat in the cable which melts the rubber insulation causing more heat and fire and the loss of your pride and joy.

the simple fix, an inline fuse AS CLOSE AS POSSIBLE to the positive terminal, that way the above scenario repeated will generate the same current but the fuse will blow, stopping the circuit and saving your car, the onle rosky part of the circuit is the part between the positive terminal and the fuse, so if that is only a few inches or less there is no chance of a car fire due to a short circuit.

so yes, it makes a huge difference guys, NEVER rely on the fuse provided internal to the amp.
Even my set up with the battery in the boot has an inline fuse with only 2 foot of cable to the amp.

hope thats clear!!

mrlee

[maxfield]

I understand all that.

So if there was a break in the cable before the fuse, the fuse would never blow due to all the current never making it that far? If that makes sense to you.

[mrLEE30]

yes if the insulation of the wire wears through in for example where it goes through the rear seat fire wall and the inner conductor of the wire touches the metal body you then have a circuit from the battery positive through the cable to the car body and back to the battery negative, this is a low resistance circuit or better known as a short circuit, the current will flow in this loop as this is the loop of least resistance and current will always prefer that route (cause its lazy like everyone else!) so it make no difference what you have connected out side this short circuit loop, and in a short circuit high current flows which creates heat and fire. by simply placing a fuse early on in the circuit, such as at the battery then it will blow once it ''sees'' high current. the fuse internal to the amp will not blow as this part of the circuit does not ''see'' any current.

So what you said is correct.

mrlee

[_bmw_316_lad_]

ya il be alright do they fuse id bout 3 inchs from the battery so i should hopefully pass that dreaded test