Diversity
Diversity in this context is all about how one establishes the maximum demand for an electrical installation or an electrical circuit. The guidelines shown here are some of those as presented in the On Site Guide. Note however that these are just that - guidelines. They are based on statistical probabilities and typical usage. As a circuit or installation designer you may choose to make different assessments of current demand based on your knowledge of the actual installation.
Note also that the figures presented here are for domestic properties only.
Allowances at point of use
The following guidelines are used when estimating the load for a particular final circuit, and shows how appliances and power points etc fed from the circuit should be accounted for:
Point of use / appliance | Current demand to be assumed |
---|---|
Other Socket outlets (i.e. not 2A or 13A) | Rated current of the socket |
2A Sockets | at least 0.5A |
Lighting outlet | Actual rating of lamp or 100W (whichever is greater) per lamp holder.
For circuits (also) supplying discharge lighting (i.e. linear fluorescent tube lights, sodium / mercury vapour lamps, or any lighting technology that requires the use of a current limiting ballast) then use VA load rating if known, since this will allows for any ballast losses and the power factor. If the VA rating of the lighting units is unknown, then use the rated wattage of the actual tubes/lamps used multiplied by 1.8 to arrive at an estimate of the VA rating for the lamp and ballast. (you can omit this step if you know all the fittings you are using contain modern HF ballasts or power factor correction). e.g. 10 x 58W Single tube linear fluorescent lamps, gives a total real power consumption of 580W. Multiply by 1.8 to give 1044 VA, and hence 4.5A |
Shaver socket, bell transformer,
electric clock point, or any appliance under 5 VA |
May be neglected for the purposes of assessment. |
Cooking appliance | 10A of total load plus 30% or remainder. Add additional 5A if cooker point socket is fitted. |
All other fixed equipment | Use nominal current as specified on the appliance ratings plate. |
Examples A lighting circuit with 6 traditional 1 lamp fittings, plus a 500W Halogen flood lamp, would be treated as 6 x 100 + 500 = 1100W or 4.8A A 2.6kW double oven, plus 6.8kW hob, and a cooker point with a fitted socket. Total load is 9.4kW or 41A peak load. Hence the diverse load is 10A + 30% of 31A + 5A for the socket = 24.3A
Allowances for Diversity
The following table is typically used for when assessing the load of a group of circuits fed from a single distribution board or CU. Note that the total current value used is the total current after diversity has been applied - not just the nominal rating of the MCB or Fuse
Purpose of circuit | Diversity applicable (domestic) | Notes |
---|---|---|
Lighting | 66% of total current | |
Heating and Power | 100% of total demand up to 10A, + 50% of the remainder. | Where space heating is connected to a general purpose power circuit. |
Cooking appliances | 100% of total demand up to 10A, + 30% of the remainder. | Add a further 5A if a socket is fitted to the cooker point. |
Water heaters (instant) | 100% of first appliance, 100% of second, and 25% of any remaining appliances. | |
Water heaters (storage) | No diversity allowable | |
Under floor heating | No diversity allowable | |
Storage Heaters | No diversity allowable | |
Standard Circuits | 100% of current demand of largest circuit. + 40% of demand for every other circuit. | These are standard final circuits as described in appendix 8 of the OSG |
Example
A domestic consumer unit with the following circuits:
Circuit No. | MCB Nominal Rating | Circuit | Design current (Ib) | Diversity Allowance | Demand after diversity |
---|---|---|---|---|---|
1. | 32A | Cooker (12kW) | 23A | 100% | 23A |
2. | 32A | Ring 1 (kitchen) | 32A | 100% | 32A |
3. | 32A | Ring 2 | 32A | 40% | 13A |
4. | 16A | Immersion heater (3kW) | 13A | 100% | 13A |
5. | 6A | Lights (1kVA) | 4.3A | 66% | 3A |
6. | 6A | Lights (600VA) | 2.6A | 66% | 2A |
Total | 86A |