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Cheap firewall passthrough

D

dmn056

Well Known Member
Friend
I've been looking at firewall passthroughs for electrical wiring, and decided I needed something like

https://www.aircraftspruce.com/catalog/elpages/firewall_penetration_kit1in.php

Unfortunately, these are very expensive, especially when converted to Australian currency and shipped half way around the world.

I don't have access to welding equipment to make something similar. However, I did find a similar-looking 304 stainless flanged pipe on eBay, at about 1/20th the ACS price.

https://www.ebay.com.au/itm/3750710...ar=644142360188&widget_ver=artemis&media=COPY

I bought a set of five of the 25mm ID x 39mm long version. Received them, sectioned one to look at the joint. Smoothed one half, pulled the other half apart with a fair amount of force required. The weld has good penetration, but only goes about half depth. Images from various positions are attached.

I think it's probably usable to form a passthrough, but I'd like to hear from anyone who knows more about it than I do whether this is a good idea or not.

Thanks for your help.
 

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dmn056 said:
I've been looking at firewall passthroughs for electrical wiring, and decided I needed something like

https://www.aircraftspruce.com/catalog/elpages/firewall_penetration_kit1in.php

Unfortunately, these are very expensive, especially when converted to Australian currency and shipped half way around the world.

I don't have access to welding equipment to make something similar. However, I did find a similar-looking 304 stainless flanged pipe on eBay, at about 1/20th the ACS price.

https://www.ebay.com.au/itm/3750710...ar=644142360188&widget_ver=artemis&media=COPY

I bought a set of five of the 25mm ID x 39mm long version. Received them, sectioned one to look at the joint. Smoothed one half, pulled the other half apart with a fair amount of force required. The weld has good penetration, but only goes about half depth. Images from various positions are attached.

I think it's probably usable to form a passthrough, but I'd like to hear from anyone who knows more about it than I do whether this is a good idea or not.

Thanks for your help.
Click to expand...
Hi Dan
I think they will "work" but suspect that they are bulkier than necessary. You could place them on firewall to see how far they protrude.

Otherwise, Bunnings have the pictured stainless flanges in 19mm or 16mm dia for less than $5 per pack of two. I have used the 19mm size fitted over a 5/8" snap bushing through the firewall. The bushing protects the wires from chafing against metal. There are three flanges on the firewall: top right and top left for sensor wires and magneto lines, and lower firewall for solenoids and feed to main bus. This provides adequate space for all the wiring. The flange can be filled with fireproof silicone or fibreglass shield to seal the gaps.
406d6b46-060d-4704-b691-ffa4079c7dc0.jpeg.jpg
20240510_100555.jpg
20240510_100622.jpg
 
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PaulvS said:
Hi Dan
I think they will "work" but suspect that they are bulkier than necessary. You could place them on firewall to see how far they protrude.

Otherwise, Bunnings have the pictured stainless flanges in 19mm or 16mm dia for less than $5 per pack of two. I have used the 19mm size fitted over a 5/8" snap bushing through the firewall. The bushing protects the wires from chafing against metal. There are three flanges on the firewall: top right and top left for sensor wires and magneto lines, and lower firewall for solenoids and feed to main bus. This provides adequate space for all the wiring. The flange can be filled with fireproof silicone or fibreglass shield to seal the gaps.
View attachment 62481
Click to expand...
Why did you not insert the OD through the hole in the firewall? Are the inside of these fittings rough? Just curious.
 
Freemasm said:
Why did you not insert the OD through the hole in the firewall? Are the inside of these fittings rough? Just curious.
Click to expand...
The inside of the fittings is smooth (since they are press-formed from a single piece of metal). They could be attached from the inside through a bigger hole, probably about 1 inch dia due to the radius at the shoulder. I'm not sure why I didn't do that, it may be because I followed the Van's plan detail for the snap bushing and then supplemented it with the extra protection of the steel flange.

One benefit is that the annular space around the snap bushing gives the firesleeve something to seat against and that helps to secure it.
 
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bjdecker said:
Can’t beat EMT fittings - Home Depot; get rid of the set screw of course.

www.homedepot.com

Halex 3/4 in. Electrical Metallic Tube (EMT) Set-Screw Connectors (5-Pack) 26272 - The Home Depot

The 3/4 in. EMT Set Screw Connectors (5-Pack) are designed to connect EMT conduit to steel outlet boxes, load centers and other metal enclosures. They are made with corrosion-resistant zinc-plated steel
www.homedepot.com
Click to expand...
There’s another version of this concept but use a saddle clamp for Romex wire. I used this with a wrap of silicone sheet as abrasion protection and clamped the saddle down. Not sure if it’s completely gas tight without sealant, but close
 
Just a quick follow up -- I prefer to drill one hole through the firewall vs 4 or more for the flanged type passthroughs.
 
bjdecker said:
Just a quick follow up -- I prefer to drill one hole through the firewall vs 4 or more for the flanged type passthroughs.
Click to expand...
You might consider that if a single wire in a bundle shorts, it will usually melt the wires around it.
 
Walt said:
You might consider that if a single wire in a bundle shorts, it will usually melt the wires around it.
Click to expand...

The number of wires in a bundle is prescribed by the amount of current carried by each wire in the bundle, if you look at the specifications for particular gauge, you will usually see "free space" and "bundled" in the current / heat rating for the wire. Plan accordingly.

For the record, I have 1 passthrough for the BFW (relay to A/C power buss), 1 for the EGT/CHT wires, 1 for the "upper" probes (OT, OP, FP, FF, Aux Gen Shunt, Aux Gen Control, Battery Indicator), 1 for the "lower" controls and probes (Shunt, Starter Enable, Master Enable, Alt Field, Alt Lamp), and 1 each for the Plasma Lightspeed 3 (dual) - sensor and coils.
 
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bjdecker said:
Just a quick follow up -- I prefer to drill one hole through the firewall vs 4 or more for the flanged type passthroughs.
Click to expand...
bjdecker said:
The number of wires in a bundle is prescribed by the amount of current carried by each wire in the bundle, if you look at the specifications for particular gauge, you will usually see "free space" and "bundled" in the current / heat rating for the wire. Plan accordingly.

For the record, I have 1 passthrough for the BFW (relay to A/C power buss), 1 for the EGT/CHT wires, 1 for the "upper" probes (OT, OP, FP, FF, Aux Gen Shunt, Aux Gen Control, Battery Indicator), 1 for the "lower" controls and probes (Shunt, Starter Enable, Master Enable, Alt Field, Alt Lamp), and 1 each for the Plasma Lightspeed 3 (dual) - sensor and coils.
Click to expand...
Guess I'm a little slow, first you said you prefer one hole then you state you have 5?

The wire bundle spec is for normal ops obviously, if for some reason one of those wires gets shorted (as I stated above), it will burn the wires bundled with it, hence never a good idea to put all your wires/eggs in one basket/bundle sort to speak.
 
Last edited:
bjdecker said:
Can’t beat EMT fittings - Home Depot; get rid of the set screw of course.

www.homedepot.com

Halex 3/4 in. Electrical Metallic Tube (EMT) Set-Screw Connectors (5-Pack) 26272 - The Home Depot

The 3/4 in. EMT Set Screw Connectors (5-Pack) are designed to connect EMT conduit to steel outlet boxes, load centers and other metal enclosures. They are made with corrosion-resistant zinc-plated steel
www.homedepot.com
Click to expand...
No judgment here—but you may want to consider that burning zinc gives off phosgene (think WW I mustard) gas.
 
Walt said:
Guess I'm a little slow, first you said you prefer one hole then you state you have 5?

The wire bundle spec is for normal ops obviously, if for some reason one of those wires gets shorted (as I stated above), it will burn the wires bundled with it, hence never a good idea to put all your wires/eggs in one basket/bundle sort to speak.
Click to expand...
The pass thru with a flange needs 5 holes, 1 big one, 4 small ones.
 
0.520 ID fits control push-pull cables. The triple matches the hole pattern for the -10. I have built similar to match RV-8.

Penetration Fittings 12-22.jpg


Insert cable or wire, pump the space full of FireBarrier 2000+ or similar, the result being gas-tight and fireproof. Or insert, pack the extra space with fiberfrax or fiberglass, then wrap in firesleeve and clamp.

Fitting and Firebarrier2000.jpg

Fitting with Firesleeve.jpg

P6010022.jpg
P6010025.jpg
 
DanH said:
0.520 ID fits control push-pull cables. The triple matches the hole pattern for the -10. I have built similar to match RV-8.

View attachment 62623

Insert cable or wire, pump the space full of FireBarrier 2000+ or similar, the result being gas-tight and fireproof. Or insert, pack the extra space with fiberfrax or fiberglass, then wrap in firesleeve and clamp.
Click to expand...
Thank you for this information. I'd be interested in getting a double fitting for my RV-8 throttle and prop cables. Don't need mixture because I'm using SDS EFI/EI. Do you have a web link for ordering them, and does it handle international orders?
 
I can make one for you, but it would be easy to do locally in Oz and save the postage.
 
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