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Heavier wiring ???

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Lotus Avatar
Lotus Silver Member Roy Hodgson
Villeneuve, VD, Switzerland   CHE
1974 MG MGB "Butterscotch"
Is there any advantage or disadvantage to using heavier wiring? My standard household wiring is 1.5mm and, according to local law can handle 13 amps at 220 volts (thus 2,860 watts). Would I have less resistance using this wire rather than the fine automotive wire? I would also have a large choice of connectors as well as thicker insulation and can get them in cables of up to 7 wires, a ready made loom.

I realize that any benefits in electrical transmission would be negated if there was any "normal" automotive wire in the circuit but having the heavier wire from, say, the battery to a relay and then to the lights or other high drawing items could be a discrete circuit.

I can get this stuff in either solid core or multi-strand and it also seems to me that it would last longer with less deterioration.

Any and all comments will be appreciated.

Roy



We have two lives. The second one starts when you realize you only have one.

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matt167 Matt D
Prattsville, NY, USA   USA
No, solid conductor wiring belongs in your house. nowwheres near a car.

That said, THHN wire, which is stranded will possibly will work, and it comes in the colors to match an MGB wiring loom. If you use something like THHN in Switzerland for home wiring, then I would say try and see but YMMV for sure.

spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Ocean Shores, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
solid wires are for stable motionless applications not for anyplace that experiences vibration or motion.

Since I am unfamiliar with wire by diameter rather than gauge, I must defer to charts posted in other threads

https://www.mgexp.com/phorum/read.php?1,3752628,3753004#msg-3753004.



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Rick Fawthrop Avatar
Rick Fawthrop Richard Fawthrop
Langley, WA, USA   USA
I have experience with metric wire.
When using the online charts for sizing the wire that you need to add the distance of the return path of the wire. For example if you have a 1.5 meter run from the headlight switch to the light you need to also include the distance from the light to the ground screw.
I believe a 2.5 mm2 wire is the equivalent to a 14 gauge wire.
Personally I would stick to the factory wiring size and color.

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MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
"Personally I would stick to the factory wiring size and color."

With the possible exception of the wire going to the heated rear screen???????????

"THHN wire, which is stranded will possibly will work, and it comes in the colors to match an MGB wiring loom"

So that'd be BS-AU7 colour coded?



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Whether selecting automotive wire size by gauge or mm, the important factors are voltage drop (current x resistance or i x R) and wire temperature in relation to the type of insulation on the wire and its temperature rating. The wire heats up with i^2 x R power loss and must dissipate that amount of power to the surrounding environment. If you have a single wire suspended in air, this power is convected/conducted into the surrounding air, but, if you bundle the wire with a bunch of other wires, like in a loom, then the problem becomes much more complicated because some heat flows from the wire to the other wires and then out into the air or into the chassis if the loom is touching the chassis.

Anyway, to keep things simple, it is best to use the same size (or larger) wires than were used in the original loom and use a wire with the same or higher temperature rated insulation.

As already posted, you'll want to use a multistrand wire for its ability to flex and withstand vibration.

In addition, you'll want the wire insulation to be at least as resistant to chaffing and cutting as the original insulation. I don't know what type of insulation was used on the OE wiring, but, it seems to strip off easily and also seems to melt at a fairly low temperature, so, I suspect any modern wire insulation would perform as well as the OE stuff. On the flip side, I wouldn't want to use a high temp PTFE insulation because it is a pain to strip unless you have heated wire strippers.

matt167 Matt D
Prattsville, NY, USA   USA
Probably not exactly the same colors, but you could certainly match colors very close.

tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
There are MANY factors on selecting wire size. The current that causes them to melt or fuse in open air is not one of them. About half of the wire in an MG is about one size too small to be efficient and only safe if the bundling and fuses are re-worked. Granted, the MG worked from the factory, but it is a terrible design. Design was to be as cheap as possible. Not picking on MG, but most cars were this bad. Standard upgrades that make a difference are the headlights, with relay added, relay for the horn, and battery cables.

The finer the strands, the more resistant to fracture with bending and vibration. I also have observed, British wire seems to be stiffer than US made wire. I question their annealing process post draw. I have seen too many wires with hidden broken strands.

Don;t be miss-led by all the color charts that show what size wire to use. That is a guide to prevent fire, not to work well. Do note SAE gauge wire is smaller than AWG gauges. Fortunately, metric is , well metric.



Cogito ergo sum periculoso

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Lotus Avatar
Lotus Silver Member Roy Hodgson
Villeneuve, VD, Switzerland   CHE
1974 MG MGB "Butterscotch"
Some very good answers. Thank you.

The consensus seems to be to use a heavier gauge of wire than original but to still use automotive multi-strand wire. Also, to check the thermal insulation properties of the insulation.

As far as colour goes, blue is blue, brown is brown, red is red etc. This is car wiring we are talking about not Ms. Markle's wedding dress.



We have two lives. The second one starts when you realize you only have one.

MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
"As far as colour goes, blue is blue, brown is brown, red is red "

Yes but Blue is only for the headlight to dipper switch, Brown is for main battery feed and Red is side and tail lamp feed.



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
If buying new wire, look for the newer cross-linked poly insulation. It will char rather than melt and does not support a flame. ( much like a lot of the white wires hidden somewhere under the dash in the harness smiling smiley ) Automotive and marine wire is UV and oil resistant. The automotive wire in the little packages at the local parts store is not the newer insulation. You can tell as it is shiny and the good stuff is very flat.

Electrons don't care about color, but it seems mechanics need them. The idea of connector 2, pin 6 to plug 8 pin 3 is too difficult. I come from a world ( computers) where all the wire was black. As we can;t easily get the striped wires, you can use a solid and then put on rings of heat shrink to keep to the color code. e.g. a red ring on a white wire for a white with red stripe ( start)

Here is a reference to a US supplier: https://www.waytekwire.com/products/1454/Automotive-Cross-Link-Wire/ They have some very good information. I am sure there is an equivalent in the EU.



Cogito ergo sum periculoso

Rick Fawthrop Avatar
Rick Fawthrop Richard Fawthrop
Langley, WA, USA   USA
Roy the real issue that needs to be addressed is the resistance in the electrical circuits.
For example, the headlight circuit. The bullit connectors, and the main light switch and dimmer are causing increased resistance and resulting voltage drop.
A relay is often added to the headlight circuit to cure this issue. The actual wire has the capacity to do the job if there was no resistance in the circuit.
A problem is the switches. The new switches are of low quality. Another problem is wire rubs and low quality replacement grommets.
The load calculations used for sizing the wire generally use a 3% resistance number. This is nowhere close to the real life resistance in a MGB.

NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
If you want to do a re-wire other than original, I would go with one of the universal hot-rod harnesses. I doubt you could buy the wire and connectors for what these cost. With the wire function written on each wire, it could not be easier to install.
After having installed a few of these in cars that had hash wiring jobs, and comparing the cost ( about $600 ) to a new Moss harness, it is the way I will be going for anything that is not a proper "restoration" to original specs.



Pete

matt167 Matt D
Prattsville, NY, USA   USA
In reply to # 3753938 by NOHOME If you want to do a re-wire other than original, I would go with one of the universal hot-rod harnesses. I doubt you could buy the wire and connectors for what these cost. With the wire function written on each wire, it could not be easier to install.
After having installed a few of these in cars that had hash wiring jobs, and comparing the cost ( about $600 ) to a new Moss harness, it is the way I will be going for anything that is not a proper "restoration" to original specs.



Pete

Do those cheap harnesses really work ok? I bought one to see what they were like and it looks usable, but not a warm and fuzzy kind of feeling with the quality. I still have the one I bought stashed away

Chalky Avatar
Chalky David White
Coventry, Warwickshire, UK   GBR
This is what I do as part of my day job.
Sizing the wire is a complex job with a lot of calculations involved. The wire size is determined by a number of factors. Current draw is one, so is the voltage drop in the wire (Ohms law). The wire will generate heat as the current passes through it (iir losses) and the wire csa, it’s insulation, and the other wires in the bundle are also factored in. As a guide current carrying capability and volt drop are the primary drivers. Make sure that the fuse that protects the cable blows before the wire is damaged (allowing for the range of voltages that you’ll see)
Use multi strand cable. Domestic single core cable will work harden and break fairly quickly in a car.
The current carrying capability of the wire is governed by how hot it can get before the insulation fails. Modern thin wall cable dissipates heat better than thick wall cable and thus has a higher current rating.
To choose the cable you need to know the current draw of the load (including in rush current) how long the cable run is and a table of cable resistances ( usually in Ohms per km). You can then work out what the volt drop in the cable is. If it’s too big increase the cable size until it’s acceptable. If the current carrying capacity of the cable is ok for your needs then you should be ok.
Remember to do your calculations using a range of voltages e.g. 12 and 14.2 to cover what will be seen in use.



Edited 1 time(s). Last edit at 2018-06-11 04:32 PM by Chalky.

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