Discuss Maximum demand - please help. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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Thanks warren, i think im going to buy a clamp meter and see what the installation is pulling at the min. Would you recomend any?

Much appreciated
 
Thank you Trebor.

The regs do state that you make an assessment of the demand and use of the installation, and include a diversity factor, when making that your calculation for maximum demand (311.1 + 313.1)
My argument was purely for domestic properties. If for example your total demand of breakers in the consumer unit was 180A and you added a diversity factor that brought it down to 120A, that is then your maximum demand, but how can you pull that through an 80A fuse?


The OSG gives ways of calculating maximum demand for differnt circuits, how is it possible to apply diversity to all MCB's when for example a shower ciruit must be taken at 100%. And i think 100A would flow through an 80A 1361 fuse for a while if nt a long time before it would trip.
 
regarding your 2 shower situation,you can get and indeed are recommended,a shower priority switch which works on current demand which effectively reduces your maximum demand.We used this on a B&B.It can also be usefull in other situations.They come in 2 types priority and non priority.One type you can nominate who has prioity,the other type is 1st come 1st served.We had to wire 4 of them thru this changeover switch.Don't know what they cost,or have a link,but I know that ABB do one and also GE.Can result in the odd cold shower but,can also pull you out of a hole regarding your demand problem
 
regarding your 2 shower situation,you can get and indeed are recommended,a shower priority switch which works on current demand which effectively reduces your maximum demand.We used this on a B&B.It can also be usefull in other situations.They come in 2 types priority and non priority.One type you can nominate who has prioity,the other type is 1st come 1st served.We had to wire 4 of them thru this changeover switch.Don't know what they cost,or have a link,but I know that ABB do one and also GE.Can result in the odd cold shower but,can also pull you out of a hole regarding your demand problem

Be interested in seeing these. Are they actually called priority switches?
 
Be interested in seeing these. Are they actually called priority switches?
Yes,warrenG,I think they are in fact known as shower prioity switches.The B&B we did was in Ireland.This wholesaler lists them www.alphaslam.ie but everything is a lot dearer in Ireland even when you allow for euro/pound,but it will maybe give you an idea.I don't see why they cant be used for other applications though.
 
Just 'Googled' it as 'shower priority switch' several links came up (the first few were Irish domains.
Incidentally, I recently installed a 'Body Drier' (Triton, I think). The manufacturer's instructions said that this could be connected to the same service as the shower. This confused me for a while until I realised that this had a built-in switch so that the two devices could not be running at the same time - first time either of us had seen such.
 
Adding all the MCB's up and then taking 40% does not work on a house like mine. It has 15 circuits. Its not a big house but has three floors and lots of small circuits. Add them all up and it goes way over. I want a quick reliable rule of thumb that I can put down on the forms.

Who the hell is going to read this **** anyway.
 
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regarding your 2 shower situation,you can get and indeed are recommended,a shower priority switch which works on current demand which effectively reduces your maximum demand.We used this on a B&B.It can also be usefull in other situations.They come in 2 types priority and non priority.One type you can nominate who has prioity,the other type is 1st come 1st served.We had to wire 4 of them thru this changeover switch.Don't know what they cost,or have a link,but I know that ABB do one and also GE.Can result in the odd cold shower but,can also pull you out of a hole regarding your demand problem


hi all

i remember these switches from the 1979 we went to pontins for a week and every time you wanted a shower you switched over from all things the cooker circuit so a butty and a shower certainly was not a thing to have.:D

now just who did i go with :rolleyes: ah parents :p

cheers all
 
A bit like the Hitch-Hikers Guide to the Galaxy the NICEIC book refers you to IEE Guidance Note 1. I'll quote anyway: "This is not, as is sometimes assumed, the rating of the electricity distributor's cut-out fuse(s). the maximum demand is a value, expressed in amperes per phase, evaluated on the basis of the connected load with an aloowance for diversity.' They say there are other methods but don't say what! Arguably, you could switch everything on and put a clamp meter on the tails. This of course would not work if the tails burn out in the process! Am I being a cowboy if I say we often just take a long hard look at what's connected, and knock 5a off the value of the cut-out? Seriously, though, if a customer asked us to connect a couple of 8 kw showers and a 6kw hob where there was a 60amp cut-out we'd say no. I was once told (on reliable authority) that the distributors rate a property at 1kw for the purposes of the network!
 
hi im about to book my nic assesment put unsure about how to work out max demand as the total number of circuit breakers exceeds to 100a main switch theres 2x 6a for lights 4x32a for sockets and ring hob 2x40a for shower and cooker and 20a for garage supply and help would be great, thanks
 
Hi.

Showers - No diversity allowable
Ring Circuits - 100% of first ring then 40% of others
Cooker - First 10A + 30% of remaining + 5A if a socket outlet
Lighting - 66% of total load of circuit.

Hope this helps.
 
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hiya thanks for tht iv added it all up but it still exceeds the 100a main switch by 36.32 would this be ok to record 136a on the certificate???
 

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