Applied plastic cement and electrical wires.

[Icra]

Hello all,

Can applied poly cement to plastic parts be dangerous if I run and clip electrical wires to the bonded surface?

More simple can hardened poly cement catch fire?

[JeffP]

It can burn, as it's essentially polystyrene.

[Icra]

It can burn, as it's essentially polystyrene.

I'm using ABS sheet with poly cement. Is this the case? A lot of electrical boxes are from ABS.

[TheSignalEngineer]

I'm not sure about that combination, but on the Big Railway we had a lot of problems caused by polymer migration when different kinds of wires and trunking were mixed. In some cases the insulation went gungy and split and others it went brittle and fell off.

 

It seems to depend on temperature and humidity as well as on the actual combination of polymers present.

[brigo]

As TheSignalEngineer says, the plasticiser in PVC cable will migrate into polystyrene "melting" it. This is the reason most electrical sockets, switches, boxes etc around the house use a thermosetting plastic such as bakelite. I would put the wiring in suitable electrical trunking.

 

Brian

[Il Grifone]

The latest electrical regulations require the consumer unit to be in a flame proof box. (We live and learn!) I try to keep dissimilar plastics (and metals) apart to avoid interaction, PVC in particular affects other plastics as already stated.

I have a Hornby Class 37 body that had grooves in the sides caused by too close proximity to coiled wire. (Not my fault - it came as part of a job lot!) She is all  restored now with only very slight ripples, which I consider OK as the prototype's panelling is never completely flat.

[timbowilts]

On reading the original post you are worried about things catching fire.

Are you seriously using wiring that is so under rated that it is going to get that hot?

If the wiring is getting even warm to the touch it is too small and should be rplaced!

 

Tim T

[Icra]

Thank you all.

I don't think my description was very clear sorry.

So on a ABS/HIPS/Styrene sheet I will put Humbrol Poly Cement over it I will put another ABS/HIPS/Styrene sheet and will become one laminate sheet. Using this sheet as a building wall I will run 12V/5V wires and maybe some DC electronics.

Knowing that on Humbrol description says that is flammable is there any risk for my assemble?

[TheSignalEngineer]

Thank you all.

I don't think my description was very clear sorry.

So on a ABS/HIPS/Styrene sheet I will put Humbrol Poly Cement over it I will put another ABS/HIPS/Styrene sheet and will become one laminate sheet. Using this sheet as a building wall I will run 12V/5V wires and maybe some DC electronics.

Knowing that on Humbrol description says that is flammable is there any risk for my assemble?

 

The poly cement is flammable because of the solvents it contains. Their job is to turn the surface of the plastic to a liquid so that the two pieces weld together just a welding steel. The solvents are highly volatile hydrocarbons. They evaporate off as the weld sets leaving it no more flammable than the original sheets.

[Icra]

The poly cement is flammable because of the solvents it contains. Their job is to turn the surface of the plastic to a liquid so that the two pieces weld together just a welding steel. The solvents are highly volatile hydrocarbons. They evaporate off as the weld sets leaving it no more flammable than the original sheets.

Does it mean that I can run wires and DC electronics without any problems?

[timbowilts]

To reiterate what I posted earlier, ONLY if the wiring is suitably sized to carry the current needed without getting warm.

 

Tim T

[DCB]

Does it mean that I can run wires and DC electronics without any problems?

No   The wires must be sized to cope with short circuit conditions.  Not just the load.  I melted the body on a class 37 when the rechargeable AA batteries on board shorted. The insulation just dripped off the wires as they glowed red hot.  If you must use this form of construction make sure you have overload protection.   1/2 amp poly switch with 1 amp wiring.   You seriously don't want a plastic model building on fire.  They are absolute sods to put out and create huge amounts of acrid smoke.

[Il Grifone]

It is always a good idea to have overload protection. You can either use a suitably rated standard 5x20 glass fuse or small lamp bulb. The latter will have a low resistance when cold, but will glow brightly and limit the current in the event of an short.

Edited October 15, 2018 by Il Grifone

[Icra]

All, thank you very much for your responses.

 

Am I correct to conclude that Styrene/HIPS/ABS don't work with any electrical montage?

Wire are one side of the story I do understand that I need to choose correct gauge, but any other electrical circuit that has capacitors or/and power inductors will be a problem because they get hot.

 

Is there any other material to use to be on the safe side?

Edited October 16, 2018 by Icra

[57xx]

Wire are one side of the story I do understand that I need to choose correct gauge, but any other electrical circuit that has capacitors or/and power inductors will be a problem because they get hot.

 

It doesn't matter whether it's wire or any other component, if it's getting hot enough to make other things to combust, then it's not spec'd correctly.

[Guy Rixon]

You have a problem with HIPS before it gets hot enough to ignite: it will distort if kept even moderately warm.

 

It's well known that HIPS can be heat-formed to shape. Heat it to the boiling point of water, form it quickly, and cool it to keep the shape. At lower temperatures, it flows more slowly under stress. I once left some models in my car on a hot day and one moulding, a Peco van, distorted completely out of shape. It was as if I'd melted it in an oven. I doubt the car temperature was above 35 celsius, and the damage happened within 24 hours. Continuous, gentle heating of a plastic structure by its lighting risks gradual damage.