RCD protected Cables under Computer Flooring?

[Krispy]

Hi All

I’m after some advice, I am doing a restaurant fit out involving a number tables that have hot pots built into the table, for customers to heat/cook their food in the hot broths or stews what have you. These are 3kw and just fed from a fuse spur.

The cable run is LSF T&E on tray laid under the computer flooring, in which there’s about 60-70mm space from the cable to finished floor level. The computer flooring is wooden tiles with a layer of sheet metal around it.

My question is, do these circuits need to be RCD protected? My worry is that as the flooring has metal components, then they may have to be RCD irrelevant of the depth (if it’s like running in walls with metal parts). But as it’s flooring, and very unlikely to have any fixings put deep enough to touch cables, is it classed differently and could the go on MCBs?

 

[James]

lets face it, if it was drawing 3kw continuously, the dam thing would be glowing in the middle of the table.

i would go with the fused spur at the table, gives a nice easy way to isolate it for cleaning etc.

i doubt it averages more than 1kw when it has reached its operating temperature.

from what i have read, i would probably be using 16A mcb or rcbo per table with an fcu for local isolation or maybe even a rotary isolator.

edit:
just noticed i have simultaneously posted almost the exat same as @davesparks
IT MUST BE RIGHT THEN!!!!

 

[davesparks]

The point was, a 2.5mm radial is ran to each hot pot, 16A radial for each. But as the tables are in pairs, with a 3m bit of 2.5mm I can link the spurs to make a ring, thous halving the amount of RCBO’s cost and saving capacity (14 single ways) on a board.

So the loads won't be evenly distributed around this 'ring'?

This just sounds like a bad, and arguably non-compliant, design to me.

2 appliances per circuit does halve the number of RCBO's yes, but it also double the number of tables out of action if a fault occurs and so doubles the losses the business makes if there is a fault.

 

[James]

So the loads won't be evenly distributed around this 'ring'?

This just sounds like a bad, and arguably non-compliant, design to me.

2 appliances per circuit does halve the number of RCBO's yes, but it also double the number of tables out of action if a fault occurs and so doubles the losses the business makes if there is a fault.

Agreed, £15 per table is not a lot in the scheme of things when if a table is out of action on a busy night you may loose £500 pet table per night.

 

[Krispy]

Agreed, £15 per table is not a lot in the scheme of things when if a table is out of action on a busy night you may loose £500 pet table per night.

So the loads won't be evenly distributed around this 'ring'?

This just sounds like a bad, and arguably non-compliant, design to me.

2 appliances per circuit does halve the number of RCBO's yes, but it also double the number of tables out of action if a fault occurs and so doubles the losses the business makes if there is a fault.

 

[Lucien Nunes]

IMO:
Plug table in under floor. Things get damaged and need to be replaced at a moment's notice. If service staff can't unplug a table they'll be swearing at you in various languages while rewiring your fused spurs with a penknife.

RCD protection and accessible isolation per table more or less essential, even without sockets. Drinks get spilled. Soup gets spilled and needs to be sponged. One day anything electric built into the table will get completely soaked.
Staff need to be able to isolate the table immediately without disturbing other customers.

Likely average load nearer 1kW per table. 3kW would see it boiling vigorously like a kettle. Typical electric hotpots are 1-2kW connected load but element rides on a thermostat. Sheathed heating elements can cause leakage but most likely in the portable appliance kind of range, unlikely to be over 1mA.

The scheme interests me because 40 years ago my family used to run the only all-fondue / table-cooked restaurant in the UK. None of these built-in electric table gubbins though. Metal (for oil) and ceramic (for cheese) fondue pots and mobile flambé station had spirit burners, fire kettles / hot pots burned charcoal, possibly the only electric devices were raclette grills. Table-cooking can bring a unique energy and sense of occasion to a restaurant. If one or two of our regular bon-vivant customers had parties in they would energise the whole place. We had years of fun but by gosh was it hard work.