Electrical queries

Question

RCD unit 65-80A.
28kw total equipment output 
(Ranger cooker 16kw, microwave 2500kw, fryer 2 X 3kw, electric griddle X 3kw etc although the range cooker will not all be switch on- so average total output could be 18-23kw

Will I need a new Consumer unit with 100a or can my old unit just need it's fuse changing?

will all the wiring needs replacing w/ a thicker ones. Will it need 16.0mm wire (to accomodate total output) if the wire touches wall/ceiling but contained in a trunk/pvc pipe?

How much time/estimated cost for this work?

Paul · Accepted Answer

In regards to your question
Your maximum demand in total of 28kw relates to  121 amps. 
As electricians, we work on what we call diversity which allows a calculation that not all appliances are on at the same time
To work this out you must first work out the amps of each piece of equipment (use ohms law - kw of appliance divided by 230 (the English voltage)) this will give you the amps of each appliance 
To calculate diversity you need the following equation
The highest amps (1 piece of equipment) + the total of all other amps for the equipment multiplied by 0.4. That will give you a total amps needed 
As for your DB it does not have a fuse just a main switch that has a specific capacity up to 100A
As for the cable 16mm can handle up to 80A if it’s 100A you need then you would need 25mm cable depending on the length of cable from the incoming power source you may need it thicker to allow for voltage drop 
As for the price 
Well that’s a visit and a detailed look at your requirements to quote you correctly and understand what work needs completing
Hope that all makes sense as it’s not as straightforward as most people think

Ross · Answer

Hello 
This would be better split into multiple circuits, 
So you don't lose all appliances if a fault was to occur

The cooker should be on its own radial circuit, likely 10mm cable on 40 amp MCB ( without working calculations myself)

Fryer and griddle are likely to be the same again
32-40 amp 10mm cable

 Microwave should be ok on a ring final circuit 32amp

And yes running new cables is likely 
I couldn't specify the method because I haven't seen the job

these sound like industrial appliances
So yes will likely need a new consumer or new consumer unit for the specific appliances high powered

Is this in a domestic dwelling or industrial?

With all that said it would have to be assessed) before anyone can give you an estimate

Also you seem to know a lot about electrics??
Thanks Ross

Ivan · Answer

Hi ideally 
The existing unit needs replacement if it’s damaged 
The maximum demand of the installation needs assessment to determine the total maximum demand after diversity applied 
So I’ll suggest fuse be upgraded to a 100A
If max demand is coming very close to 100A ideally needs a 3phase supply 
If cables pass the dead test could be used without replacement rewiring 
I’ll suggest a condition report to be done prior to any decisions made 
I’m on  if you need any consultation 
Thanks

Matthew · Answer

This is very hard to explain without manufacturers instructions. 
You can apply diversity to the appliances. For explaining the range cooker manufacturers instruction could advise 30 amp breaker and a 6mm twin and earth cable. However, it could also advise a higher breaker and cable size. 

An electrician would split up the above appliance into different circuits and apply diversity. 

If it is calculated you need a bigger fuse coming into the property the DNO needs to be contacted to increase the fuse size. If you increase the fuse size the meter tails will need to increase. 

Depending on the property a board change, fitting isolator, increasing meter tails and checking all the circuits are safe can take up to a day to a day and a half depending on the property. 

The cost will vary in the UK depends where you are located from anywhere from 700 to 1500 for a full RCBO board. 

You really need an electrician to attend the property to give you an idea of what needs to be done. 

Thanks

Gary · Answer

No idea (price) until the job is looked at on-site and diversity of circuits and loads are taken into account, if upgraded wiring is required then a new consumer unit will be required to comply with current wiring regulations. If you need an upgrade on your main fuse ( which sounds like it more than likely need one) to 100 Amp the maximum you can get as a standard domestic supply this will have to be done through your electricity supplier as it can not be done by any electrician. Some supply companies charge for this and will have to be booked well in advance of your other electrical work

Joshua · Answer

Typically the main breaker size will be calculated based upon the supply cable cross-section size. 
It would likely be best to get an electrician to take a look at your supply cable to determine for sure its cross-sectional area.

The cost to replace a consumer unit depends on a few factors, the largest two probably being how many circuits are there (how many different fuses/breakers) will give you a good idea of this and if your tails/incomer cables need upgrading also will affect the cost.

Making a few assumptions based upon the info provided.

A typical medium/large sized consumer replacement (8-14 circuits) would cost around £400-£750, it may be slightly more if your Incoming cables need upgrading also or if there are any other complicating factors

Hope this helps
Kind regards
Josh J.J. Electrical

Antony · Answer

Hi this job would have 2 have a site visit 2 see exactly what needs doing no proper sparky could give you a quote without looking at it first

Bill · Answer

This is a question that can’t be answered without seeing the installation but I would say you need to upgrade the mains 
But as I said this is something that can’t be answered without seeing the installation

Freddie · Answer

Hi I would recommend 
Updating consumer unit to a new dual rcd with 80amp rcds 

I’m gathering your kitchen wiring would need upgrading better to pull a 10mm cooker radial circuit.

And a new kitchen ring Main circuit 

Ideally would need to look to be able to give you a quote please contact me

Freddie sparks

Sam · Answer

You don't necessarily need to get a new consumer unit, depending on the one that is in place now, you can just change the main switch. You will need at least one space for the cooker as that will need its own feed with isolation, 16-25mm depending on the cable run. The other items could be put on a ring main with isolation as they are all around 13amp but that's me assuming the microwave is 2.5 kw as for the time and price of the job I would need to see the job. Thanks, Sam please feel free to call me to discuss further.

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