Differences in silicone? Dow Corning #4 compared to 100% GE Silicone

[USAeng]

We have an old drawing that said to use Dow Corning #4 Insulating Compound to cover a few connections in a power supply... recently I noticed that the shop is using waterproof window/door/attic/basement 100% silicone... the kind you can get at lowes for your home... is this an adequate replacement in your opinion?

I will call Dow Corning and ask... but not sure how honest they will be about the comparison. That is, I assume they will try and say their product is superior just to sell it... Thanks.

 

[USAeng]

The directions on the old drawing say exactly: "apply Dow Corning #4 Insulating Compound to all eposed areas at least 0.010" thick, where an electrical discharge may occur"

 

[MikeHalloran]

Dow #4 is like a grease. It doesn't change or cure in service.

AFAIK, all/most of the silicones sold at Lowes are caulking. They dispense like grease and cure into rubber shortly after application.

Common silicone rtv formulations release acetic acid during cure. You may notice the vinegar odor. It's real vinegar, and will corrode electrical connections. Not good in a power supply, or anything else electrical.


The special RTVs specifically formulated for use in electrical service use a different cure mechanism, and don't release acetic acid.

Some of those electrical silicone RTVs are 'self-leveling', which means they ooze out for a while (until you breathe on them), then cure into a rubber that stays shiny and wet-looking. Those in particular make really zoomy covers/ strain reliefs for electrical work. Once cured, they don't just wipe off, and they're not all that easy to cut off, either.





Mike Halloran
Pembroke Pines, FL, USA

 

[Comcokid]

Obviously a silicon designed for electronics insulating properties is tested for it's dielectric strength, and insulating properties over time, temperature, aging, etc.

A household caulk - even one stated as 100% silicone, is not 100%, but will have some additives for UV exposure, and blended to a viscosity and properties to make it easy to apply in a home construction environment.

I recently took apart a 1.5kw off-brand made-in-china power inverter, and found some really poor construction. Among other things lots of silicon caulk were used - the type for bathtub caulk filled with lots of gypsum/chalk and other fillers.

 

[USAeng]

Thanks guys.... with this info and some tips from a call to GE I am now getting the correct stuff.

GE sales confirmed that the acetic acid could be bad on some of our connections that are copper and brass.... they said that the household silicone would be ok to use as an insulator on harder metal electrical connections though... for whatever thats worth coming from a sales person from GE...

We will be using the real electrical compound from now on...

Have a good one!

 

[MacGyverS2000]

Someone in the shop should be taken out back and given a good whacking for making that kind of substitution...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[USAeng]

tell me about it... it happens way too often... its like they think "now what would Lowes have that would work?" rather than question why someone had a specific product/design/instruction on the drawing or specification.... like they were using red loctite to seal npt threads... or using 1000V rated wire on 3000v because they figured the 1000v had a built in factor of safety that would be high enough... crazy

 

[USAeng]

oh and the solidworks guy would take all the old drawings with specific grades of steel and changes it to CS or SS... I just started here a few months ago... they havent had an engineer for the past 10 years, so its stuff they just didnt think was important

 

[LionelHutz]

Is there a UL file or something similar for the product? If so, I bet you were in violation there too, as the file would likely specify the compound.

 

[MagicSmoker]

Before you guys break out the pitchforks...

USAeng - What sort of power supply are we talking about here, and what is the silicone actually being used for? I mean, using it to dampen vibration on a tall through-hole component is obviously less critical than protecting against corona/arcing from a solder joint on a pc board.

At any rate, the type of silicone preferred for electronic uses releases methanol and ammonia when it cures rather than acetic acid. Silicone is highly resistant to damage from UV all on its own so it is not necessarily the case that anything was added to the "100% Silicone" from a home improvement store to make it more UV resistant.

No comment on the appropriateness (or lack thereof) in using non-approved products/components....

 

[USAeng]

It is to prevent arcing from a 2000V spark gap to any other electrical components that may come near the connections on either side of that component. In this case I would say that the Dow Corning #4 would be a superior product to GE's Silicone I from the home improvement store... the silicone II would be better I guess it dries without releasing as much acid, but the contacts are brass, so #4 Dow Corning is better and for the quantity used not that much more expensive... further more, the drawing calls it out so it should be a no brainer for these guys to use the right stuff

Thanks again for all the comments