Discussion
A bit of background first, I'm building a mid-engined kit car using a 1992 Toyota/Lexus 1UZ-FE (a 4l V8), due to space limitations I'm losing the twin distributors and going to Coil-On-Plugs (COP).
It's come to the time I'm thinking about making up some wiring and I have a dilemma with the temperature ratings of the wiring, common thinwall is rated to 105C (with excursions to 120C), Connectors are rated to 125C. The wiring for the COPs will be enclosed in the grove in the cam cover with a plate over the top to hold the COPs in place.
Now I'm thinking that while 105C *should* be fine it could get mighty hot in that enclosed space and I'd be better off with higher rated wiring (eg 125C-150C).
The questions I have are:
1) Am I over thinking this, being an idiot and 105C will be fine?
2) If not will silicon wiring (rated to 150C-200C) be fine?
3) If not any suggestions for the best wiring to get and where from (in small amounts not 100m reels)?
It's come to the time I'm thinking about making up some wiring and I have a dilemma with the temperature ratings of the wiring, common thinwall is rated to 105C (with excursions to 120C), Connectors are rated to 125C. The wiring for the COPs will be enclosed in the grove in the cam cover with a plate over the top to hold the COPs in place.
Now I'm thinking that while 105C *should* be fine it could get mighty hot in that enclosed space and I'd be better off with higher rated wiring (eg 125C-150C).
The questions I have are:
1) Am I over thinking this, being an idiot and 105C will be fine?
2) If not will silicon wiring (rated to 150C-200C) be fine?
3) If not any suggestions for the best wiring to get and where from (in small amounts not 100m reels)?
You're not overthinking anything, you're actually doing the job properly.
As a guide, I have seen many looms reach 145C during heat soak.
These guys would be a good source of wiring products:-
http://www.vehicle-wiring-products.eu/VWP-onlinest...
As a guide, I have seen many looms reach 145C during heat soak.
These guys would be a good source of wiring products:-
http://www.vehicle-wiring-products.eu/VWP-onlinest...
You probably need to understand a bit more about what the 105degC limit actually is!
Is it the point that the insulation fails ? (at what ever test voltage the wire is rated too (and that might be several hundred volts)
Is it the point at which the insulation discolours? (often the case)
Is it the point at which it looses its mechanical strength?
How long can the wire experience this high temperature before it fails its tests?
Generally speaking, for most std wiring products, the maximum quoted temperature is the long term temperature which the manufacturer suggests is not likely to lead to long term degredation of the insulation system. This obviously must include the omhmic heating from the current the wire is carrying also. In your application the only real direct failure that matters is a direct contact short, that would require a large crack or delamination to occur in the wiring (because of the low voltage nature of your system). Depending on how well anchored your loom is, you might want to consider its scuff and vibration resistance too. One way of improving the wire spec cheaply for localised sections of a loom is to sheath the wire in a high temperature heat shrink cover. You could also use a heat reflective sheath to help slow the upheat, although in this case, the bulk heat transfer will be conductive and most likely to occur under engine-off hot soak conditions.
My recommendation, use a "standard" wiring of the highest quoted temperature resistance easily availible, make sure any high current carrying conductors are generously sized (not normally an issue for coils due to there transient charging nature), wrap wires in a suitable heat shrink, and make sure they are very well mechanically secured (Engine born vibrations, even for a V8 can be very large indeed)
Is it the point that the insulation fails ? (at what ever test voltage the wire is rated too (and that might be several hundred volts)
Is it the point at which the insulation discolours? (often the case)
Is it the point at which it looses its mechanical strength?
How long can the wire experience this high temperature before it fails its tests?
Generally speaking, for most std wiring products, the maximum quoted temperature is the long term temperature which the manufacturer suggests is not likely to lead to long term degredation of the insulation system. This obviously must include the omhmic heating from the current the wire is carrying also. In your application the only real direct failure that matters is a direct contact short, that would require a large crack or delamination to occur in the wiring (because of the low voltage nature of your system). Depending on how well anchored your loom is, you might want to consider its scuff and vibration resistance too. One way of improving the wire spec cheaply for localised sections of a loom is to sheath the wire in a high temperature heat shrink cover. You could also use a heat reflective sheath to help slow the upheat, although in this case, the bulk heat transfer will be conductive and most likely to occur under engine-off hot soak conditions.
My recommendation, use a "standard" wiring of the highest quoted temperature resistance easily availible, make sure any high current carrying conductors are generously sized (not normally an issue for coils due to there transient charging nature), wrap wires in a suitable heat shrink, and make sure they are very well mechanically secured (Engine born vibrations, even for a V8 can be very large indeed)
Edited by anonymous-user on Monday 25th February 15:21
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