How are you calculating maximum demand

[Ohm Check]

How are you calculating maximum demand for the certificate and what should you do if your calculations exceed the main fuse rating?

 

[Rockingit]

How are you calculating maximum demand for the certificate and what should you do if your calculations exceed the main fuse rating?

Well, you'd start by using the guidlines in the OSG. What makes you think that your actual demand is going to exceed intake?

 

[buzzlightyear]

did we have some body here that showed the diversity calculation .

 

[buzzlightyear]

Lighting - 66% of total current demand for each circuit
Power - 100% of the first ring circuit + 40% of all other circuits
Cooker - 10A + 30% of remaing rated current + 5% if the CCU has a socket outlet
Shower - No diversity allowable
Instantaneous water heater - 100% of largest heater + 100% of second largest + 25% of of any others
Thermostatically controlled water heater - No diversity allowable
Underfloor heating - No diversity allowable

 

[GBDamo]

How are you calculating maximum demand for the certificate and what should you do if your calculations exceed the main fuse rating?

What are you determining the demand for?

Domestic - use the OSG. It's written to cover an average domestic dwelling.

Commercial - use your noggin. You need to have a decent understanding of the end use and from there can determine your own realistic demand.

Industrial - above my pay grade and limits , although I'd guess it would be somebody much better paid's responsibility.

 

[nicebutdim]

Domestic - use the OSG. It's written to cover an average domestic dwelling.

I find the IET have some work to do on this, in order to catch up with their own recommendations, as maximum demand can be far exceeded in a modern installtion, where multiple radials are wired for power and to individual appliances.

 

[Rockingit]

I find the IET have some work to do on this, in order to catch up with their own recommendations, as maximum demand can be far exceeded in a modern installtion, where multiple radials are wired for power and to individual appliances.

I'm not sure I instantly agree with that. Just because we're now far more in-tune with running separate supply circuits to avoid the risk of hotspots on general circuits doesn't mean that either the number of high current using appliances has grown or that the appliances themselves have grown - if anything the opposite is true. Even when you factor in things like EV points, overall diversity stays the same because that's a predominantly overnight (and in itself time limited) load.

The average house may now be packed full of gizmo's but they each draw mW and gone are the days of 3kW kettles and three bar fires.

 

[Pretty Mouth]

I'm not sure I instantly agree with that. Just because we're now far more in-tune with running separate supply circuits to avoid the risk of hotspots on general circuits doesn't mean that either the number of high current using appliances has grown or that the appliances themselves have grown - if anything the opposite is true. Even when you factor in things like EV points, overall diversity stays the same because that's a predominantly overnight (and in itself time limited) load.

The average house may now be packed full of gizmo's but they each draw mW and gone are the days of 3kW kettles and three bar fires.

I very much agree with what you say here. Problem is, this isn't really reflected in the guidance in appendix A of the OSG, which I think was the point @nicebutdim was making. OSG guidance gives a higher max demand for an installation that has numerous circuits vs. an installation that has fewer circuits, all other things being equal.

 

[nicebutdim]

I'm not sure I instantly agree with that. Just because we're now far more in-tune with running separate supply circuits to avoid the risk of hotspots on general circuits doesn't mean that either the number of high current using appliances has grown or that the appliances themselves have grown - if anything the opposite is true. Even when you factor in things like EV points, overall diversity stays the same because that's a predominantly overnight (and in itself time limited) load.

The average house may now be packed full of gizmo's but they each draw mW and gone are the days of 3kW kettles and three bar fires.

The average house may well be packed with gizmos, but think through the point I'm making.

You can approach a rewire from many different directions. Depending on how circuits are divided, maximum demand can vary greatly without any difference in total current drawn.

Split general power from 2 rings to 4 or 5 radials. Take a number of appliances which could be supplied from an rfc and give them their own radial circuit.

I've completed a couple of rewires for customers who liked the idea of dividing existing power arrangements and this saw a considerable rise in maximum demand, despite no additional power being drawn in those properties. In fact one would have drawn a little less power than before as lighting upgrades and replacement of appliances made the house a bit more efficient.

 

[Scintillam]

What are you determining the demand for?

Domestic - use the OSG. It's written to cover an average domestic dwelling.

Commercial - use your noggin. You need to have a decent understanding of the end use and from there can determine your own realistic demand.

Industrial - above my pay grade and limits , although I'd guess it would be somebody much better paid's responsibility.

Max demand can normally be pulled from the meter on existing installations for commercial/industrial meters, cycle through the readings- its sometimes hidden on the second screen of readings which need a long press of the button to access