I want to run some wiring from underneath the van up the vent space behind the fridge (185 ltr Dometic) into an overhead cupboard. Is there anything at the back of the fridge that would be hot enough to melt any wiring sheath should it touch? Thanks.
Cheers, John.
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"My mind is made up. Please don't confuse me with facts."
Strange as it may seem conduit can de rate wire amperage . Yes just saddle it away . Mainly for mechanical protection . If 3 way fridge ? . Away from gas heater section . Should be enough ventelation to prevent heat build up . Theres shielding on hot areas on fridge . As said with clearance youll be fine !
-- Edited by Aus-Kiwi on Saturday 16th of December 2017 01:16:29 PM
-- Edited by Aus-Kiwi on Saturday 16th of December 2017 01:17:34 PM
Running the wires through some flexible conduit, and using plastic saddles to keep the conduit in place, will stop any chaffing of the wires, as well as melting
On the top of my smaller Dometic 3 way fridge there was a sign, (did not see it until the fridge was removed)
Keep wires away from the boiler area, or words to that effect
I have run wires up the back of mine to run computer fans on the condenser fins to help with summer in Qld. There should be an air space between the frige rear and van outerskin. Just keep it away from hot elements eg tubes to Condenser and Gas flue. Sika or silicon glue or cable ties will do the job.
Strange as it may seem conduit can de rate wire amperage . Yes just saddle it away . Mainly for mechanical protection . If 3 way fridge ? . Away from gas heater section . Should be enough ventelation to prevent heat build up . Theres shielding on hot areas on fridge . As said with clearance youll be fine !
-- Edited by Aus-Kiwi on Saturday 16th of December 2017 01:16:29 PM
-- Edited by Aus-Kiwi on Saturday 16th of December 2017 01:17:34 PM
Never herd of that before
so does that mean if you put say a cable in a conduit that is only capable of carrying 10 amps it will only carry say 8 amps before it melts . Or has some clown come up with a rule saying that you must use a larger amp wire than is needed if you run it in a conduit .
If I can work out how to do it I will test that one out .
dibs
-- Edited by mr glassies on Wednesday 20th of December 2017 10:31:51 PM
The cable in conduit derating is legit but more related to 240vac cabling than solar cabling because of the difference in acceptable voltage drop. On 240vac stuff 5% is quite acceptable, on solar cabling 1.5% is excessive, voltage drop is the result of resistance within the conductor and rsistance creates heat. So the derating is due to the heat being trapped inside the conduit, the same or greater derating needs to be applied to cables exposed to a high ambient temp such as experienced behind an older style fridge with the condenser mounted on the back of the fridge or a 3 way boiler condenser set up. The heat generated from the sides of a modern fridge with the condenser in the walls is so small it wouldn't be worth doing the math to calculate it as long as the cable does not interfere with the clear airflow up the sides of the fridge body.
T1 Terry
__________________
You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.
Any links to any sites or products is not an endorsement by me or do I gain any financial reward for such links
Strange as it may seem conduit can de rate wire amperage . Yes just saddle it away . Mainly for mechanical protection . If 3 way fridge ? . Away from gas heater section . Should be enough ventelation to prevent heat build up . Theres shielding on hot areas on fridge . As said with clearance youll be fine !
Never herd of that before
so does that mean if you put say a cable in a conduit that is only capable of carrying 10 amps it will only carry say 8 amps before it melts . Or has some clown come up with a rule saying that you must use a larger amp wire than is needed if you run it in a conduit .
You probably have not heard of it as you are not an electrician. You are correct in you summation that covering a cable prevents the heat from escaping and thus it will take less current to melt as cable. When electricians are designing an installation they do not refer to cable sizes by their current carrying capacity but by the copper size in those cables. They then use tables to find out what size wire will carry the rated current they are designing around. The more cables in a bunch the larger the copper size they require. There are different tables for different situations like bundled cables in the open air, bundled cables in walls and cables in conduits.
The current ratings attributed to household cables is their ratings in a wall cavity or open air. The lack of knowledge of things like this is what is one of the reasons that non-electricians get involved in arguments on the subject and make those stupid statements that lead to arguments. You folk should listen to what PeterQ (Oldtrack) and others that have worked in the industry tell you.
The saving grace with our caravan installations is we do not design our systems by using the open air ratings of our cables (or should not.) If you use the current carrying capacity of the cable is used it will result in too much voltage drop in the lengths of cables you find around our rigs. If you design your cabling for a maximum of 3% voltage drop (the common recommendation) then you will end up using cable many times the current rating than it needs to be for the danger of the cables melting.
Therefore there is little danger of overheating cables in caravans if you have cabling installed for a minimum of voltage drop no matter where you install the cables.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
Thanks for the assistance. I turned the fridge on 240v and looked in the rear of the fridge from the vents. The pipes that snake back and forth at the back of the fridge for the top half and then go through cooling fins at the top get really hot. Too hot to keep you hand on. I have saddled/silconed my new wires away from these hot pipes now. Still wondering though if they might be hot enough to melt wire sheathings if they were to lie next to them?
Cheers, John.
__________________
"My mind is made up. Please don't confuse me with facts."
Yes thatās why overhead mains are bare wire . Securing the wire AWAY from heat is important . Just saying just running in conduit on
Itās own may not help ?? If itās double insulated? It only really just needs saddling ., A simple heat shield would help . BTW many old buildings in Sydney have 6mm sq wire feeding a whole house . Itās in open air . Short circuit distance and low amperage CBās in vans helps the situation . Keep in mind it gets very hot in roofs also .,
Well after it got explained to me it all became clear hahah . I had herd of it before but wasnt thinking when I read it . Thanks for all the explanations . I should have known as I had been told yrs ago when contracting to Energex . But because it was erelivante to my work it didnt stay in the memory bank or not out the front any way . But if you dont ask ya dont learn a .
Dibs
-- Edited by mr glassies on Friday 22nd of December 2017 08:29:26 AM
Yes thatās why overhead mains are bare wire . Securing the wire AWAY from heat is important . Just saying just running in conduit on Itās own may not help ?? If itās double insulated? It only really just needs saddling ., A simple heat shield would help . BTW many old buildings in Sydney have 6mm sq wire feeding a whole house . Itās in open air . Short circuit distance and low amperage CBās in vans helps the situation . Keep in mind it gets very hot in roofs also .,
It's one of those cases of the conduit acting as a heat shield rather than a mechanical barrier to keep heat out because the cabling is of a sufficient size to eliminate excess heat generation inside the cabling insulation so air cooling is not required.
One of the other major concerns is when polystyrene is added to the outside of fridge walls to improve the fridge performance. Some polystyrene attacks the plasticises in the cable insulation and actually strip the insulation from the cables, a serious risk in RV roof insulation as well. You will see this sometimes with imported electrical goods where the electrical cord has stuck to the polystyrene packaging and some of the white poly ends up a permanent marker on the cable, it's not glue, it is the poly melting into the cable insulation.
T1 Terry
__________________
You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning.
Any links to any sites or products is not an endorsement by me or do I gain any financial reward for such links
Yes itās not so much the heat generally in rear of fridge . Itās the gas area ., Mind you it takes in hell bend etc to actually get anywhere near the hot area, plus itās pretty well shielded . We my old one was . Moved onto compressor fridge . Best thing we ever did !! . Simply running the wire to the left side would give a heap of clearance . If well vented like it should be ? There should be no issues ., As with most these things . Thereās so many variables . Keep in mind the heat capability of conduit ? Yes itās mainly to hold wire away from heat .
