Max demand on a unit

[Spoon242]

Guys,

I have been asked to calculate the maximum demand for a DNO who want the information before upgrading the metering to 3 phase. The client has 3 phase coming in to the building but only single phase meter.
The building is a small commercial warehouse unit (4m x 6M) with some upstairs and downstair offices next to it.

They have two DB's

Can I use as in the 'Calculations for Electricians and Designs' book, 100% largest + 50% for commercial. Similar to how we use domestic 100% largest +40%

DB1 100A board

C20 - External lights
B10 - Internal lights + WC
C20 - WC Water Heater
C20 - WC Hand dryer
C16 - Fire Alarm

=53A

DB2 100A board

B32 - Ring
B32 - Ring
B32 - Ring
C6 - Alarm
B16 - Heater
B16 - Heater
B16 - Heater
C10 - Warehouse lights
B10 - Lights
B10 - Lights
C20 - Battery Charger

=116A (this is too much):sad_smile:

Am I getting really confused here?

The whole job started as being asked to install a 3 phase socket for a 32A battery charger.

I then have to convert it to kw for there application form, please let me tap in to your experiences once again, thanks in advance.

 

[ackbarthestar]

I wouldn't bother with the OSG, you'll go round in circles. To do the job properly you will need to estimate what loads are likely to be used at any one time period and for how long your loads will operate. There are different methods of making a reasonable estimate of maximum demand and diversity.

You could just quote the maximum available for a 3-phase supply covered by 100A/phase.

I think, also, you will need to provide a KVA value as opposed to kW

Single phase = 23kVA (230 * 100)
or
3-phase = 70kVA (rt3 * 400 * 100)

 

[Spoon242]

I wouldn't bother with the OSG, you'll go round in circles. To do the job properly you will need to estimate what loads are likely to be used at any one time period and for how long your loads will operate. There are different methods of making a reasonable estimate of maximum demand and diversity.

You could just quote the maximum available for a 3-phase supply covered by 100A/phase.

I think, also, you will need to provide a KVA value as opposed to kW

Single phase = 23kVA (230 * 100)
or
3-phase = 70kVA (rt3 * 400 * 100)

Thanks for the reply. They defiantly want it in kw's. I will try and scan in the form they need filling out later. To make my ramblings clearer.

 

[Knobhead]

Use some common sense. No way are any of those circuits are going to take the loading listed.

Diversity calculations are a load of male bovine excrement.

 

[Spoon242]

I have been trying to get the file attachment work, but it keeps going to error. I will look for a different way to share it later

 

[UKMeterman]

Hi,
Is this an existing install? Have they been popping the main fuse? If not then they are not takeing a right lot then. If you want to get a true figure then hire in an energy anylyzer for a week and do a report for your client.

 

[steveberry11]

Guys,

I have been asked to calculate the maximum demand for a DNO who want the information before upgrading the metering to 3 phase. The client has 3 phase coming in to the building but only single phase meter.
The building is a small commercial warehouse unit (4m x 6M) with some upstairs and downstair offices next to it.




They have two DB's

Can I use as in the 'Calculations for Electricians and Designs' book, 100% largest + 50% for commercial. Similar to how we use domestic 100% largest +40%

DB1 100A board

C20 - External lights
B10 - Internal lights + WC
C20 - WC Water Heater
C20 - WC Hand dryer
C16 - Fire Alarm

=53A

DB2 100A board

B32 - Ring
B32 - Ring
B32 - Ring
C6 - Alarm
B16 - Heater
B16 - Heater
B16 - Heater
C10 - Warehouse lights
B10 - Lights
B10 - Lights
C20 - Battery Charger

=116A (this is too much):sad_smile:

Am I getting really confused here?

The whole job started as being asked to install a 3 phase socket for a 32A battery charger.

I then have to convert it to kw for there application form, please let me tap in to your experiences once again, thanks in advance.

Do use the OSG as a guide but you are able to make ajudgment call using your experience and knowledge of the site.

You should use the connected loads for all but ring mains but you can make ajudgment on this. You may know that there are 10 sockets with computers pluggedin to everyone. Or high load equipment in every one. Make a call.

DB1
Using the OSG. I have not included the alarms as they have a negligible load.
18+9+20+12=59A

DB2
32+16+16+16+32+9+9+20=130A

These readings may be a bit high but you have given the MCB size not totalconnected load.
The battery charger may only be used at night when the premises are empty if sodon't include it.
The outside lighting may also be used at night when the premises are empty ifso don't include it.

It is a judgment but you must base it on good theory the OSG is a very goodstarting place.

GOOD LUCK

 

[Engineer54]

Do use the OSG as a guide but you are able to make ajudgment call using your experience and knowledge of the site.

You should use the connected loads for all but ring mains but you can make ajudgment on this. You may know that there are 10 sockets with computers pluggedin to everyone. Or high load equipment in every one. Make a call.

DB1
Using the OSG. I have not included the alarms as they have a negligible load.
18+9+20+12=59A

DB2
32+16+16+16+32+9+9+20=130A

These readings may be a bit high but you have given the MCB size not totalconnected load.
The battery charger may only be used at night when the premises are empty if sodon't include it.
The outside lighting may also be used at night when the premises are empty ifso don't include it.

It is a judgment but you must base it on good theory the OSG is a very goodstarting place.

GOOD LUCK

And that little lot is ''Exactly'' why no-one with any experience uses the OSG!! lol!!

 

[Spoon242]

Can I use as in the 'Calculations for Electricians and Designs' book, 100% largest + 50% for commercial. Similar to how we use domestic 100% largest +40%

DB1 100A board

C20 - External lights
B10 - Internal lights + WC
C20 - WC Water Heater
C20 - WC Hand dryer
C16 - Fire Alarm

=53A

DB2 100A board

B32 - Ring
B32 - Ring
B32 - Ring
C6 - Alarm
B16 - Heater
B16 - Heater
B16 - Heater
C10 - Warehouse lights
B10 - Lights
B10 - Lights
C20 - Battery Charger

=116A (this is too much):sad_smile:

As you can see I had not quoted OSG, rather Calculations for Electricians and Designers, *Amended spelling mistake this time, LOL.* I think I have been working it out correctly based on calculations taken from estimated values for demand factors.

Where it stats, The maximum demand of an installation P max is the sum of the loads installed Pi multiplied by a demand factor g

P max = g x Pi

Pi - is total installed load for the installation considered, being the sum of the loads directly connected, generally on the basis of continuous duty.

g - is the demand factor, that is the ratio of the maximum demand of an installation to the corresponding total installed load.

I then covert the total current in to kilo watts for the purposes of the form they asked for using ohms law