swa fuse rating

[ricicle]

they quite often use 2 or 3 cables in large mains installs simply because they either don't do cable large enough, or that if they did it's not flexible enough to be bent to fit..

I always wondered why they don't do this anyway since 2 cables can take more current than the equivalent size can..

ie 10mm² can take 46A so that's 92A for double.. but 25mm² can only take 80A

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please excuse any typos, I'm typing with 2 plasters on my fingers..

Our factory kitchen has a paralleled supply 2 x 95mm²!!

 

[Taylortwocities]

You must have a very big fat fryer!!

 

[RF Lighting]

You must have a very big fat fryer!!

He doesn't look very fat to me

 

[thespook]

Done all the work the cable is now buried under concrete about a foot down. RCD fitted at both ends. I thought about putting some warning signs up (danger buried cable) attached to the house wall and also on a small wall that the cable is buried next to, do you think it is necessary or is it overkill. The signs are only 100x75mm
Thanks

 

[bernardgreen]

You must have a very big fat fryer!!

He doesn't look very fat to me

Looks more like a chip monk

 

[davy_owen_88]

You should have placed warning tape above the cable along it's entire length to let people who are digging know it is there.

 

[bernardgreen]

I always wondered why they don't do this anyway since 2 cables can take more current than the equivalent size can..

Because if one cable fails open circuit everything still works OK except that voltage drop is probably over the limit and the single remaining cable is "protected" by an MCB or fuse that is over the maximum carry capability of the single cable.

ie 10mm² can take 46A so that's 92A for double.. but 25mm² can only take 80A

The 2 off 10mm² has a larger surface area per unit of cross section than the single 25mm² so can dissapate more heat

10mm² radius = 1.78mm circumference = 11.2mm

25mm² radius = 2.8mm circumference = 17.7mm

so two of 10mm² have 22.4mm of effective area

No guarantee the maths are accurate

 

[LondonRay]

I make the 2nd one 17.6mm

but then I do need to get out a lot more !

 

[ColJack]

same thing can be said of a ring though bernard..

if a live cable breaks or comes loose from a socket, then you have up to 32A running down one leg..

 

[bernardgreen]

same thing can be said of a ring though bernard..

if a live cable breaks or comes loose from a socket, then you have up to 32A running down one leg..

Probably the only dis-advantage of a ring main.

 

[davy_owen_88]

The reason it will work in a ring circuit and not for a shower/cooker or meter tails is due to the fact a ring circuit is not continually loaded, and the load is distributed around it. If continuity is broken it's unlikely the full 32A will travel down a single conductor, and if it did, it would be for a short length of time and only a small-ish overload.

Now compare that to a shower which is a single load and you use 2x 4mm² cables. If one comes loose the other cable is definitely going to end up carrying the full load and it's likely to be a substantial overload at that.

I'm assuming that risk is the main reason parallel cables are only used when it is absolutely necessary.

 

[ColJack]

In a house of 1 or 2 people then it's not unreasonable to assume that the shower will only be used for 30mins to and hour a day..

what are the odds of breaking a cable once installed anyway?