Ask Your Question

Angie's List Answers is the trusted spot to ask home improvement and health questions and get answers from service companies, health providers and consumers. For ratings and reviews on companies in your area, search Angie's List.

Top 30 Days Experts
Rank Leader Points*
1 kstreett 240
2 Guest_9020487 110
3 Guest_9190926 105
4 GoldenKid 100
5 ahowell 95
6 KnowledgeBase 95
7 skbloom 80
8 Guest_98024861 70
9 Guest_9311297 70
10 Guest_9400529 70

*Updates every 4 hours

Browse Projects By Category

Question DetailsAsked on 7/9/2014

Can I spray foam insulate the conduit openings in service panels?

I have a 200 amp service panel which has a drop to another outside box for the shed and hot tub. I am getting an extreme amount of cold air leaking into these in the winter. Is it safe to insulate the interior openings of the 200 amp box and drop conduit box with spray foam?

Do you have the same question? Follow this Question

3 Answers

Voted Best Answer

Absolutely NO - for several reasons

1) normal spray foam has chemicals in it including solvents and formaldehyde which dissolve the insulation on electrical wiring - ditto to caulks

2) putting foam in there will thermally insulate the wiring, potentially causing it to heat up more than it should. Conduits are sized to provide a certain amount of air space around the cables running through them, and if that airspace is eliminated the cables can overheat in use - fires due to this are not uncommon where people fillthe counduit to capacity with wires

3) normal foams are quite combustible and have a high flame spread rating - any foam used in an electrical system has to have low flame spread rating

There are special foams designed to seal conduit against water and vermin which do not hurt the cable - when using them, it is critical to encapsulate the smallest length of conduit possible so minimize the "hot spot" you are forming in the cable.

There are also conduit fittings that slip over the cable (so has to be free end) and screw into a threaded conduit fitting and tighten around the cable to seal it.

Better solution for you, especially since only doing one place - There are plugs designed for this purpose (actually more to keep insects and watter out, but serve the same purpose) available at electrical supply houses to fit each specific size of conduit and cable; and duct seal compound available for under $10 - here is an Amazon link showing some of those products -

In your case the putty or injector tube type is probably best, because most of the plug types are for installation while doing the wiring, not after the fact,thought there are some split grommet types you can slip on after the fact - called panel grommets (for exactly what you are doing) and fire stop bushings, which are designed to stop fire from passing through conduits.

Allofthe above are avaiulable at electrical supply houses - but you will need to know cable size and conduit size for all but the jelly and putty types of solution.

Remember - limit it to just the shortest length of conduit filling feasible to reduce the length of cable exposed to limited cooling.

Answered 5 years ago by LCD


Many thanks for the links and useful info. Limiting the plug to an inch or so in depth suffice?

Answered 5 years ago by Matty49


I spaced a bit on this one - forgot you are only after cold air flow, so you could just stuff 1/4" or so of fiberglass fiber (without any paper or foil) into the end of the conduit just by itself - or stuff a bit of fiberglass in there 1/4" or so and then seal with the conduit sealant/putty for a truly positive seal. I bet the fiberglass (steal a bit off some exposed fiberglass btting somewhere) would probably work fine by itself, negating the need to buy anything.

For a water seal you usually go in 1/2 inch or so.

Answered 5 years ago by LCD


Yes you can use FOAM that does not attack cables. The product that I use for my utility is

DUCTOLOX 431. You will have to search it online. Can't remember their contact info. This product is made to expand, seal and not attack cables. They also have spray version of this called DUCTOLOX 419 which you can use. My utility uses it for conduit and duct sealing of water and air.

Answered 5 years ago by manny

Related Questions

Terms Of Use
Privacy Policy