Heated Rear Screen - What Cable Amps?
Discussion
phillpot said:
I'd suggest a minimum 2mm or 28/0.3mm (17.5A) cable although half the elements are probably broken so something thinner would do 
It was compromised anyway by using the tailgate gas struts to tie the feed to the demister; simplest way to find out, identify the demister fuse and add 50% to its rating and find cable adequate for that 
Tasmins had a thermal cutout for the demister on the fuse/relay panel, incidentally.
Wedg1e said:
phillpot said:
I'd suggest a minimum 2mm or 28/0.3mm (17.5A) cable although half the elements are probably broken so something thinner would do
It was compromised anyway by using the tailgate gas struts to tie the feed to the demister; simplest way to find out, identify the demister fuse and add 50% to its rating and find cable adequate for that Tasmins had a thermal cutout for the demister on the fuse/relay panel, incidentally.
You first need to understand that circuits are fused above their up to temperature current draw ratings
For instance, lets look at a heated rear window circuit
Lets use some ficticous current draw ratings (current draw ratings vary from screen to screen, manufacture to manufacturer)
HRS Current Draw When Hot = 12 Amps
HRS Current Draw When Cold = 15 Amps
Fuse Rating must be above 15 Amps
Manufacturer Fitted Fuse = 20 Amps
Cable 28 x 0.30 Current Draw Rating = 17.5 Amps
HRS Manufacturer Cable Size Used = 28 x 0.30
Using Your Method
Manufacturer Fitted Fuse = 20 Amps + 50% = 30 Amps
Your Suggested cable Size = 65 0.30 That has a current rating of 35 Amps
You have just created a wiring harness that is close to 2.5 times bigger and heavier than it should be
Do you often give good advice like this?
Penelope Stopit said:
This is hilarious, you are not even close to how the calculation should be carried out
You first need to understand that circuits are fused above their up to temperature current draw ratings
For instance, lets look at a heated rear window circuit
Lets use some ficticous current draw ratings (current draw ratings vary from screen to screen, manufacture to manufacturer)
HRS Current Draw When Hot = 12 Amps
HRS Current Draw When Cold = 15 Amps
Fuse Rating must be above 15 Amps
Manufacturer Fitted Fuse = 20 Amps
Cable 28 x 0.30 Current Draw Rating = 17.5 Amps
HRS Manufacturer Cable Size Used = 28 x 0.30
Using Your Method
Manufacturer Fitted Fuse = 20 Amps + 50% = 30 Amps
Your Suggested cable Size = 65 0.30 That has a current rating of 35 Amps
You have just created a wiring harness that is close to 2.5 times bigger and heavier than it should be
Do you often give good advice like this?
Who are you Penelope Stopit? Are you a Wedge or TVR owner? Will you be attending this years Big Bad Wedge fest so you can give frank and useful advice to those that need it? I am not knocking your technical information but the way you phrase your replies is a little caustic and unnecessary and I'm not sure why that is? Having had a quick glance back at some of the other threads you have participated in this does seem to be the norm for you. Politeness doesn't cost. Thank you.You first need to understand that circuits are fused above their up to temperature current draw ratings
For instance, lets look at a heated rear window circuit
Lets use some ficticous current draw ratings (current draw ratings vary from screen to screen, manufacture to manufacturer)
HRS Current Draw When Hot = 12 Amps
HRS Current Draw When Cold = 15 Amps
Fuse Rating must be above 15 Amps
Manufacturer Fitted Fuse = 20 Amps
Cable 28 x 0.30 Current Draw Rating = 17.5 Amps
HRS Manufacturer Cable Size Used = 28 x 0.30
Using Your Method
Manufacturer Fitted Fuse = 20 Amps + 50% = 30 Amps
Your Suggested cable Size = 65 0.30 That has a current rating of 35 Amps
You have just created a wiring harness that is close to 2.5 times bigger and heavier than it should be
Do you often give good advice like this?
KKson said:
Who are you Penelope Stopit? Are you a Wedge or TVR owner? Will you be attending this years Big Bad Wedge fest so you can give frank and useful advice to those that need it? I am not knocking your technical information but the way you phrase your replies is a little caustic and unnecessary and I'm not sure why that is? Having had a quick glance back at some of the other threads you have participated in this does seem to be the norm for you. Politeness doesn't cost. Thank you.
I apologise if I come across as a badun.I can't think of a polite way to inform someone that they are typing a load of b
ksWell, anyway, just to close this one off; for some obscure reason, TVR took the live feed to the HRS from the driver’s side sill all the way across the body to the passenger ‘B’ post and then to the HRS and earthed the HRS elements back on the driver’s ‘B’ post. I just reversed it and cut out most of the surplus wire which meant I had plenty of cable* to do the job and it didn’t cost me a penny. My favorite type of solution. 
- I have of course assumed TVR used the correct type of cable in the first place. It is heavier than most of the other stuff in the loom and as it hasn't gone up in flames yet I'm keeping my fingers crossed
Penelope Stopit said:
This is hilarious, you are not even close to how the calculation should be carried out
....
Do you often give good advice like this?
Did you miss the ....
Do you often give good advice like this?
at the end of my post?Regardless, whatever rating of fuse the circuit NEEDS, the cable should be rated to handle more than that otherwise (especially in a slow-heating scenario such as, let's say, a nice low-resistance heating element on the end of 15 feet of wire) the cable can melt before the fuse blows. But then you'd know that, I'll just state it for those who don't.
Edited by Wedg1e on Monday 27th February 19:58
Gassing Station | Wedges | Top of Page | What's New | My Stuff