Derating wiring ampacity that is buried in insulation

[jmedclay]

It occurred to me that burying my wiring in foam would cause an increase in temperature and possibly the need to reduce the allowable current. The only question was "by how much". Have any of you looked into that? I'm will this weekend, since I'm on the verge of installing the final insulation around my wiring, but if any of you have been there already, please sing out.

I'm using 90C Ancor wiring, individual conductors in braided loom.

[bobhenry]

OH LORDY LORDY

Yet another pitfall in the wonderful world of electrics.

but are we certain that by burying the wire in insulation we are trapping heat in or perhaps we are preventing heat from migrating into the wire from the ambient summer heat.

OH LORDT LORDY what shall I do !

[absolutsnwbrdr]

Unless you are pulling 1.21 gigiwatts through your flux capacitor, the heat generated by the electrical transmission of your 12V system is negligable.



Go camping and enjoy you weekend

[madjack]

Unless you are pulling 1.21 gigiwatts through your flux capacitor, the heat generated by the electrical transmission of your 12V system is negligable.



Go camping and enjoy you weekend

..."is negligible", if properly sized in the first place ..........................................

[absolutsnwbrdr]

..."is negligible", if properly sized in the first place ..........................................

Ah this is true. Thanks qualifying that!

[Engineer Guy]

Open air vs. bundled Wire capacities are duly noted over time as different. See 2 References below, with a concise quote from the 1st Website.

Wire Capacity Chart

Open Air vs. Bundles and/or Conduits

Heat is the primary determiner of the maximum amount of power any wire can carry, and the ability of that wire to dissipate that heat has a large impact on the final rating. Wires that are run in bundles (such as in a wiring harness or wiring conduit) cannot dissipate heat as easily as a single wire run in "open air", and as such must be "de-rated" to less than their maximum value to account for this. Also, wires that are run in areas that are unusually hot (such as in an attic or in an engine compartment) may need similar de-ratings. If both situations are encountered together (bundled wires in an unusually hot environment) then you need to de-rate for both factors and the capacity is further reduced.

AWG Wire Chart & Calculator

As with Safety Chain ratings, or any number of issues, the only person you need to satisfy in your wiring designs is you. I'm in favor of over-Engineering, so I hope this 3rd Party info helps.

My own saying below reflects my view on this issue as to whether or not to take note of basic Physics like heat production in closed areas.

[bobhenry]

WOW! I DONE GOOD !


Ran 12 gage stranded to feed the clearance and tails. I am good to 60 amps per side

[eamarquardt]

If you remember the 66 and earlier VWs their lights tended to dim with the age of the vehicle because they were 6 volt systems and the wiring wasn't quite heavy enough for the amps that were flowing. Over time the resistance of the wire was permanently increased to the point the lights dimmed.

As I understand it, the reason it is against the "code" to run romex through conduit is because of the possibility of heat build up.

Keep your loads light and and use reasonable sized conductors.

I routinely push over 200 amps through a #12 wire but the wire is water cooled, ha.

A good approach is to measure the voltage of your wiring run at the source and again at the load to see how much loss you're seeing in your wiring. Here is a good discussion:

http://www.psihq.com/iread/faqvolt.htm


Cheers,

Gus

[Thawley]

..."is negligible", if properly sized in the first place..........................................

Agreed.

Not only that, but you still have fuses or breakers if there is any problem. (You do have fuses or breakers, right?)

.

[eamarquardt]

WOW! I DONE GOOD !


Ran 12 gage stranded to feed the clearance and tails. I am good to 60 amps per side

How do you figure 60 amps?

Cheers,

Gus

[jmedclay]

Thanks Engineer Guy (we are brothers). I suspect that it's not a problem given the particulars of what I've done and list anecdotal evidence. I think my eyes saw something in an article (NEC or IEEE) that indicated no de-rating necessary if using 90C wire within the limits published for the gauge but it was over my shoulder as I left for work. Edit: The previous sentence is incorrect - I did not interpret what I glanced at correctly and temperature based derating from the otherwise maximum capacity is always necessary. End of edit. I'll post what I find later for thems that might be interested.

I do like your sig. Physics doesn't care a whit.

[jmedclay]

Thanks Engineer Guy (we are brothers). I suspect that it's not a problem given the particulars of what I've done and list anecdotal evidence. Snipped. I'll post what I find later for thems that might be interested.

I do like your sig. Physics doesn't care a whit.

Some handy links, Ancor wire tech info, a relevant NEC paragraph and NEC tables, respectively.

http://www.marinco.com/page/allowable-amperage
http://www.inspectionnews.net/home_insp ... ation.html
http://www.houwire.com/products/technic ... le310.html

Correcting and adding to previous info:
I'm using Ancor 105C wire, not 90C
12g for the 20A, 120V AC circuits.
14g for the DC circuits that are fused at 10A or less.

My wiring/fusing is fine after derating for encapsulation, but I read enough to know that one could easily make a quality electrical system that was code compliant until adjusting for the effects of insulation and ambient temp. I also read enough to see that the temperature rise of thermally insulated conductors can be substantial, particularly in areas of high ambient temperature or solar gain and long duration, heavy use. Short duration use of higher current devices like hot plates/toaster ovens helps prevent unwanted outcomes, but thats a little too random for my taste.

It's time to finish the insulation installation. I am eager to get the front/roof skin installed.

Latest pics, not yet in my gallery, here: http://www.flickr.com/photos/21624415@N ... 017251243/

[dh]

WOW! I DONE GOOD !


Ran 12 gage stranded to feed the clearance and tails. I am good to 60 amps per side

How do you figure 60 amps?

Cheers,

Gus

20 amps per wire?

[dh]

And I though I was playing it safe running16g to my LED porch lights and LED dome light...

[Dale M.]

I only hope that these wire connections (splices) are for "mock-up" and not permanent...



Dale