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

1

12345aob

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Under "PARTICULARS OF INSTALLATION REFERRED TO IN THE CERTIFICATE" maximum demand (load)...................kva/Amps

Do I put in the whole load for the house or just the load for the new circuit I have added?

I have just put in an outside switched socket and two 150w swiched floods. less that 15 amps in total.

Also has the 17th been amended yet?
 
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1

12345aob

  • Thread Starter Thread Starter
  • #2
Under "PARTICULARS OF INSTALLATION REFERRED TO IN THE CERTIFICATE" maximum demand (load)...................kva/Amps

Do I put in the whole load for the house or just the load for the new circuit I have added?

I have just put in an outside switched socket and two 150w swiched floods. less that 15 amps in total.

Also has the 17th been amended yet?
17th has not been amended. maximim demand if for the whole house.
 
C

coxy

  • Thread Starter Thread Starter
  • #3
Hi,
What you need is a clamp meter get the house holders permission and turn all major appliancies and take a reading then apply diversity.
 
J

Jurassic Spark

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  • #4
You can ASSUME a max demand of 80amps - same as the cut-out fuse size.
 
M

maddfridge

  • Thread Starter Thread Starter
  • #6
I concur maybe 100amp though, only problem is finding out what the fuse size is without cuting the seal on cutout.[/quote


Hi all
diversity = maxiumum demand / connected load !

so someone may have designed the house with future additional loading allowed you need to assess the whole house loading first then see what amps you are theortically pulling. take the reading see what the difference is if it to much up the service cut out fuse assuming all circuits will meet bs7671 for volt drop etc.

fun this diversity and max demand is it not

doing 2391-20 its mind blowing !!!!!!!!!!

cheer all
 
E

ezzzekiel

  • Thread Starter Thread Starter
  • #7
as a quick guide adding up all breakers in use and taking 40% will give you an estimated demand
 

Des 56

-
Arms
Esteemed
The way I see it is that you ascertain wether the system can carry the additional load initially
You install the additional circuit The certificate is then applicable to that circuit only
So the max demand is then the load of that single addition
Otherwise you could have a single circuit certificate for say a 8Kw shower with a max demand of maybe 80amp on the cert
 
S

sparkymaz

  • Thread Starter Thread Starter
  • #9
Calculating max. demand, i am up to 145A with diversity taken into account. all notices on boards say max current should not exceed 100A. Demand with dirversity on 2x 40A (showers) 3x32A (ring main) and 1x16A Radial takes me to 114A already. Just seems high to me, am i calculating right? if so what are the implications? I heard someone say you can assume 100A as thats what the main incoming fuse/main switch is rated at. Is this right?
 
N

Nutter

  • Thread Starter Thread Starter
  • #10
Hi all. Maximum demand for domestic testing is the incoming fuse size, ie, 60A, 80A or 100A, depending on what is fitted. That’s what I put on the test results. The demand on the main fuse takes into account that every electrical item will not be switched on and used at exactly the same time. Most electrical items have a higher start current for a few seconds, and then drop back down to a lower than rated current when running. And don’t forget, you can’t pull more amps than the main fuse is rated at!
 
M

maddfridge

  • Thread Starter Thread Starter
  • #11
Hi all. Maximum demand for domestic testing is the incoming fuse size, ie, 60A, 80A or 100A, depending on what is fitted. That’s what I put on the test results. The demand on the main fuse takes into account that every electrical item will not be switched on and used at exactly the same time. Most electrical items have a higher start current for a few seconds, and then drop back down to a lower than rated current when running. And don’t forget, you can’t pull more amps than the main fuse is rated at!

on site guide gives guidance which really should be taken in to account then completely burnt and common sense used.

it is all down to what is needed for that installation with allowing for future growth or use but who know what it will be used for in a weeks time to a years time.

look at the number odf outlet points and make a calcualted judgement and think to add for future growth

wiil the sub mains take a 100 amp fuse ?? just basing it on fuse size is a good methos but will the supply cable carry the future load. in all installations whats coming in through the floor tells you what you can and cannot do anyone agree . if it aint big enough to cope make it bigger ??

design exam on tuesday helppppppppppppppppp!!!!

must be mad cheers all
 
T

trebor

  • Thread Starter Thread Starter
  • #12
Hi all. Maximum demand for domestic testing is the incoming fuse size, ie, 60A, 80A or 100A, depending on what is fitted. That’s what I put on the test results. The demand on the main fuse takes into account that every electrical item will not be switched on and used at exactly the same time. Most electrical items have a higher start current for a few seconds, and then drop back down to a lower than rated current when running. And don’t forget, you can’t pull more amps than the main fuse is rated at!
what utter tosh, you do not use the main fuse rating as md even if you think you know it, a carrier can be marked as 100 amps and have a 60 amp fuse fitted.

im afraid if i was assessing you for 2391 using the main fuse figure would be a fail

read your osg it has a clear tabulated guide to calculating md
 
M

maddfridge

  • Thread Starter Thread Starter
  • #13
hi trebor

when you do the design project the onsite stuff just does not work after all the on site guide is just that a guide.

you have to look at the oveall loads and allow a common sense diversity against known standards. Doing this now some showers tradinitonal are up to 10kw power showers are as low as 150 watts
trition
Voltage 230/240v Ac. Rating 150W nominal Temperature Control Manual
Plumbing System Compatibility Gravity hot & cold only Inlet Connections
15mm push fit Water Entry Points Rising, falling, back Outlet Connection
1/2” BSP Minimum Head Pressure 75mm Maximum Head Pressure 10m Maximum Open Outlet Flowrate 14l/min Exposed Wall Mounted Only

Approvals BEAB, CE, BKM guarantee year
AS2000x integral pump power shower

The reason is because the hot water is pulled off the super duper gas fired water heater thingy not the old combi type. stuff like that so just looking at loading is a good method against the fuse sizestarting point to see where the loading can be reduced or increased a drop like that from 30 amps to 45 amps. no immersion heater no tank so there another 13 etc get the general gist

cheers

ps the exam was a right Bast**D selv every where will have to wait for feb to find out meantime project
 
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N

Nutter

  • Thread Starter Thread Starter
  • #14
what utter tosh, you do not use the main fuse rating as md even if you think you know it, a carrier can be marked as 100 amps and have a 60 amp fuse fitted.

im afraid if i was assessing you for 2391 using the main fuse figure would be a fail

read your osg it has a clear tabulated guide to calculating md



Thank you Trebor.
Fortunately for me I have 2391 and thankfully, you didn’t assess me!
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 other point that you made about the fuse carrier, in my opinion, anyone who is not prepared to pull out the main fuse and open it up to see what the fuse rating is should not be testing. First, you do not guess what is in the carrier. Second, how do you know the tails are the correct size for the fuse? And finally, you must have safe isolation of the system you are working on to comply with the Electricity at work regs (reg 13)
 
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D

Dave

  • Thread Starter Thread Starter
  • #15
what utter tosh, you do not use the main fuse rating as md even if you think you know it, a carrier can be marked as 100 amps and have a 60 amp fuse fitted.

im afraid if i was assessing you for 2391 using the main fuse figure would be a fail

read your osg it has a clear tabulated guide to calculating md
You can put your point forward without being offensive....please remember this next time before you hit your enter key...
 

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