running wiring next to polystyrene

[Hannah and Jay]

Above the gunwales our boat is insulated with good old polystyrene behind the T&G, we want to run cable for the lighting behind this but I've heard that it shouldn't be done as overtime the polystyrene can "react" with the cable and cause unwanted problems, is this true? And if so, is there a special type of cable that you can use for this purpose as we don't really want ugly wires running to lights on top of the T&G and there isn't really the space to fit any housing plus wire behind the T&G.....

[jonny]

Above the gunwales our boat is insulated with good old polystyrene behind the T&G, we want to run cable for the lighting behind this but I've heard that it shouldn't be done as overtime the polystyrene can "react" with the cable and cause unwanted problems, is this true? And if so, is there a special type of cable that you can use for this purpose as we don't really want ugly wires running to lights on top of the T&G and there isn't really the space to fit any housing plus wire behind the T&G.....

Yes what youve been told is correct don't do it!,if youve got polystyene behind the boards then you should be able to run a 'conduit' to shield your cables, garden hose will protect your cables and is relatively easy to push behind the boards

[blackrose]

Above the gunwales our boat is insulated with good old polystyrene behind the T&G, we want to run cable for the lighting behind this but I've heard that it shouldn't be done as overtime the polystyrene can "react" with the cable and cause unwanted problems, is this true? And if so, is there a special type of cable that you can use for this purpose as we don't really want ugly wires running to lights on top of the T&G and there isn't really the space to fit any housing plus wire behind the T&G.....

 

Yes it's true. PVC coated cables can react with EPS. Put the cables in flexible conduit and then run them under the lining. I guess to be sure you should check the conduit isn't also made of PVC?

 

http://www.vehicle-wiring-products.eu/VWP-onlinestore/sleeving/sleeving.php

 

The flexible convoluted tubing is the one you want - made from nylon. I think it's available slit which makes it easier to put your cables inside - or just run a stanley knife down the length.

Edited August 30, 2011 by blackrose

[nb Innisfree]

Allegedly, modern pvc cabling doesn't react with polystyrene but I wouldn't risk it, use a conduit.

[MtB]

Allegedly, modern pvc cabling doesn't react with polystyrene but I wouldn't risk it, use a conduit.

 

I fix boilers for a living and there is one particular boiler I specialise in fixing.

 

I see from five to ten of this specific boiler each week and in the factory they are assembled with a PVC cable draped across loosely across the polystyrene insulation of the heat exchanger. On every boiler I see the cable appears to have 'melted' a deep channel into the polystyrene insulation. It looks as though the cable has been getting really hot but it can't be - it only carries micro-amps of digital data.

 

If I need to pull the cable out there is only ever damage to the polystyrene, never the cable, the cable always appreas fine. I therefore conclude there is little risk to PVC cables, only to the polystyrene they are in contact with.

 

These boilers range from 10 years old down to about four, by the way. I dunno if brand new PVC cable no longer does this.

 

Mike

[blackrose]

I fix boilers for a living and there is one particular boiler I specialise in fixing.

 

I see from five to ten of this specific boiler each week and in the factory they are assembled with a PVC cable draped across loosely across the polystyrene insulation of the heat exchanger. On every boiler I see the cable appears to have 'melted' a deep channel into the polystyrene insulation. It looks as though the cable has been getting really hot but it can't be - it only carries micro-amps of digital data.

 

If I need to pull the cable out there is only ever damage to the polystyrene, never the cable, the cable always appreas fine. I therefore conclude there is little risk to PVC cables, only to the polystyrene they are in contact with.

 

These boilers range from 10 years old down to about four, by the way. I dunno if brand new PVC cable no longer does this.

 

Mike

 

Yes, I've also heard that the EPS tends to shrink back from the cable which means that the PVC on the cable is left unaffected. However if there's any possibility of a reaction it just isn't worth the risk.

[Gibbo]

The reaction between the EPS and the cable is a leaching reaction whereby a plasticiser from the PVC comes out of the cable insulation and melts the EPS. This leads people to believe that only the EPS is bothered by it. What it actually does is leave the PVC brittle and it eventually cracks and splits.

[Phoenix_V]

The reaction between the EPS and the cable is a leaching reaction whereby a plasticiser from the PVC comes out of the cable insulation and melts the EPS. This leads people to believe that only the EPS is bothered by it. What it actually does is leave the PVC brittle and it eventually cracks and splits.

I've removed damaged pvc cable that had been run near polystyrene.

[mayalld]

I fix boilers for a living and there is one particular boiler I specialise in fixing.

 

I see from five to ten of this specific boiler each week and in the factory they are assembled with a PVC cable draped across loosely across the polystyrene insulation of the heat exchanger. On every boiler I see the cable appears to have 'melted' a deep channel into the polystyrene insulation. It looks as though the cable has been getting really hot but it can't be - it only carries micro-amps of digital data.

 

If I need to pull the cable out there is only ever damage to the polystyrene, never the cable, the cable always appreas fine. I therefore conclude there is little risk to PVC cables, only to the polystyrene they are in contact with.

 

These boilers range from 10 years old down to about four, by the way. I dunno if brand new PVC cable no longer does this.

 

Mike

 

I'm afraid that your conclusions are flawed.

 

PVC cable that has been in contact with expanded polystyrene can indeed LOOK fine.

 

However, the polystyrene has been turned to "goo" by the plasticiser from the PVC.

 

The plasticiser is what makes the PVC supple. Effectively, the PVC has dried out, and gone hard. It is now brittle.

 

That may not be an issue with boilers, but in an environment like a boat, where there can be significant vibration, brittle PVC will break up leaving bare wires.

[DHutch]

Bringing up an old thread, but I understand the cables in our boat (single wires) are butyl rubber, although you cant really tell from looking at them, but they where selected as being safe with polystyrene.

 

I am however struggling to buy any more of the stuff, bar immersion heater flex....

 

 

Daniel

[Glynn]

You could put this over the new cable, comes in loads of sizes.

 

http://www.maplin.co.uk/p/d-line-cable-tidy-tube-black-11m-n59ku

[Alan de Enfield]

Specialists will sell, what is called "non-migratory PVC Cable".

 

We used to manufacture it and supply it to the "Brown Goods" industry as the cases of TVs, Radios etc etc were made from a form of Polystyrene (not the expanded stuff you will be familiar with) and after a few fires as a result of the cable shorting out as a result of touching the 'case' it became the norm to use non-migratory PVC, or to use a nylon bushing.

 

Alternatively use a Nylon conduit - do NOT use garden hose as that is PVC

[John V]

cables insulated in XLPE are suitable for use when in contact with polystyrene (6491AX) they do singles of var sizes but you would have to check which wholesalers stock it

[Alan de Enfield]

cables insulated in XLPE are suitable for use when in contact with polystyrene (6491AX) they do singles of var sizes but you would have to check which wholesalers stock it

 

The 6491X (AX) are not flexible cables, they are stranded, but NOT classed as flexible.

 

Example 2.5mm² is 7/0.67mm (7 strands each being 0.67mm diameter)

 

"Flexible" cables to BS6500 (2.5mm²) is 50/0.25 ( 50 strands each being 0.25mm diameter)

 

6491X (AX) is very stiff, has a much larger bending radius and will not withstand flexing or vibration like the 'Flexible' (2491X) BS6500 type

[Arthur Brown]

Any cable of suitable construction marked LSZH would be good - means low smoke zero halogen therefore it cannot contain PVC.

Any cable of suitable construction marked H07RNF or H05RNF would be good -usually to be found in three core types up to 125A for stage use.