Shower Wiring in Granny Annexe

[MechEng]

Hi All,

I am Faraz, I'm a Mechanical Project Engineer by trade. This is my first post on these forums.

I am looking for some insight into a problem I'm having.

I currently have a 6mm Cable running from the main RCD to a 9.8kW shower in a Granny Annexe. the wire currently runs about 25m long to the Annexe and is run underground from the main property. Now I've always opposed to having a 6mm cable for this application but my father was adamant 6mm was plenty and thus installed it. I believe its a 30A RCD. The shower constantly trips (not surprised) and can't be used for more than 2mins at best before it trips.

For a cable length of <5m I would personally go for 10mm cable and 45A fuse. But I feel that due to the length it would make more sense to go upto a 16mm cable due to the length.

Is 16mm SWA cable overkill? Is 10mm SWA fit for purpose? Average shower time is 15mins total.

Please note this Annexe was a shed before and so I am in the process of correcting the wiring according to the local council's safety regs.

 

[telectrix]

10mm cable is the correct size for your application, as long as it's not buried in insulation, 16mm is overkill and you'll not be able to terminate it. is it the MCB that trips or the RCD? a 32A MCB is too low a rating for 9.8kW.

10mm cable, 50A MCB is my solution.

 

[Pete999]

Hi All,

I am Faraz, I'm a Mechanical Project Engineer by trade. This is my first post on these forums.

I am looking for some insight into a problem I'm having.

I currently have a 6mm Cable running from the main RCD to a 9.8kW shower in a Granny Annexe. the wire currently runs about 25m long to the Annexe and is run underground from the main property. Now I've always opposed to having a 6mm cable for this application but my father was adamant 6mm was plenty and thus installed it. I believe its a 30A RCD. The shower constantly trips (not surprised) and can't be used for more than 2mins at best before it trips.

For a cable length of <5m I would personally go for 10mm cable and 45A fuse. But I feel that due to the length it would make more sense to go upto a 16mm cable due to the length.

Is 16mm SWA cable overkill? Is 10mm SWA fit for purpose? Average shower time is 15mins total.

Please note this Annexe was a shed before and so I am in the process of correcting the wiring according to the local council's safety regs.

Do the calculations and go by that guessing is the wrong way.

 

[Taylortwocities]

Think you need to get some terms correct.

What do you mean by a “main RCD”

I don’t think you mean a 30amp RCD. Perhaps you mean MCB??
RCDs and MCBs are very different things, and you’ll get wrong or confusing advice if you don’t use the right words.

Maybe better for you to post a photo and indicate which device trips.

 

[Pete999]

Hi All,

I am Faraz, I'm a Mechanical Project Engineer by trade. This is my first post on these forums.

I am looking for some insight into a problem I'm having.

I currently have a 6mm Cable running from the main RCD to a 9.8kW shower in a Granny Annexe. the wire currently runs about 25m long to the Annexe and is run underground from the main property. Now I've always opposed to having a 6mm cable for this application but my father was adamant 6mm was plenty and thus installed it. I believe its a 30A RCD. The shower constantly trips (not surprised) and can't be used for more than 2mins at best before it trips.

For a cable length of <5m I would personally go for 10mm cable and 45A fuse. But I feel that due to the length it would make more sense to go upto a 16mm cable due to the length.

Is 16mm SWA cable overkill? Is 10mm SWA fit for purpose? Average shower time is 15mins total.

Please note this Annexe was a shed before and so I am in the process of correcting the wiring according to the local council's safety regs.

ypu should be ensuring the wiring complies with BS 7671 mate, not the Council's safety regs whatever they are

 

[Taylortwocities]

Even with the tripping, I kinda think the vd is too much using 6mill

 

[MechEng]

Do the calculations and go by that guessing is the wrong way.

What I told my dad too... I tend to ponder though.
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Think you need to get some terms correct.

What do you mean by a “main RCD”

I don’t think you mean a 30amp RCD. Perhaps you mean MCB??
RCDs and MCBs are very different things, and you’ll get wrong or confusing advice if you don’t use the right words.

Maybe better for you to post a photo and indicate which device trips.

You're right, I did mean 30A MCB. Realised my mistake when I read the post again.

Fixed RCD on the consumer unit. And there are some MCBs for different circuits around the house, Separate one for the Shower (which is the one that trips). I'll try and get a photo tonight.