Radial length

[Farmelectrics]

Ok just a quick one got brane freeze here a 20a radial can be no more than 50m2 so if this is a straight run what length is it basically how do you convert square metre into metres in a straight run thanks in advance

 

[worzol99]

I think its divide by 2 so 25 meters.

 

[Farmelectrics]

Thanks worzol Sunday night not got thinking cap on lol

 

[Octopus]

Well... the square root of 50 is just over 7 so 7 x 4 = 28


I'm guessing this is right!

 

[Farmelectrics]

Ok Murdoch that's another way to do it then square root it and then times by 4 gives a more accurate figure thanks anyone got any other ways of working it out

 

[HandySparks]

It's the floor area that matters. ie, the area of the rooms served by the circuit.

 

[Octopus]

It's the floor area that matters. ie, the area of the rooms served by the circuit.

Yes, but I think the OP has it in mind to have a long radial with one outlet on it so the "floor area" is a bit irrelevent!

 

[kingeri]

Agreed, the total length of the circuit depends on how long the run to the CU is!

Edit: The whole "area served" way of doing things is a bit dated IMHO, I'd just calculate the max. length permitted given the type of cable I wanted to use..

 

[HandySparks]

Yes, but I think the OP has it in mind to have a long radial with one outlet on it so the "floor area" is a bit irrelevent!

If it's only one outlet, then yes. If it's a general purpose 20A socket radial as shown in Appendix 15, then the maximum area served is a guide, based (I understand) on the amount of energy that can reasonably be used in a given space. Obviously, this doesn't apply to radial circuits for specific items such as water heaters, etc.

 

[kingeri]

For socket circuits, it all comes down to how many heaters are likely to be plugged in. How many homes these days use convector heaters as their comprehensive heating solution?

 

[Guitarist]

Just use the resistance charts to calculate the maximum zs you are allowed.

 

[Beavstro]

I would think it depends what's on the end of the radial... Volt drop etc would need to be calculated regardless of the square meter values.

 

[Guitarist]

If it's for a general socket outlet, then assume maximum current.

 

[Richard Burns]

Table 7.1 in the OSG gives the maximum lengths of standard circuits; for a 20A type B 2.5/1.5 radial, volt drop limits it to 31m.

 

[alanl]

I think it is poor that many cannot work out the maximum length of a circuit by calculating the volt drop and potential Zs of a circuit.

These calculations are really simple, and should be second nature to a working electrician - even asking what the max. length should be is wrong, as all the details are easily available for standard circuits in the OSG. if one is 'mathematically challenged'.

 

[Guitarist]

I think it is poor that many cannot work out the maximum length of a circuit by calculating the volt drop and potential Zs of a circuit.

These calculations are really simple, and should be second nature to a working electrician - even asking what the max. length should be is wrong, as all the details are easily available for standard circuits in the OSG. if one is 'mathematically challenged'.

You're talking to many guys who still don't know how to test an RFC correctly....

 

[DPG]

I always rest my RFCs. They get tired after supplying all those appliances. Daz

 

[Lucien Nunes]

These calculations are really simple, and should be second nature to a working electrician

Absolutely. I'm not having a go at the OP but the first few posts of the thread really had me scratching my head! Totally separate considerations - the area served which governs whether the circuit is likely to fulfil the user's power consumption needs, and the length of the cable that governs the loop impedance and voltage drop, i.e. safety and efficiency of the circuit. The latter can be addressed by a larger cable for a given size of circuit, the former only by more or larger circuits.

BTW can anyone tell me how to convert amps into pints?

 

[Guest111]

Absolutely. I'm not having a go at the OP but the first few posts of the thread really had me scratching my head! Totally separate considerations - the area served which governs whether the circuit is likely to fulfil the user's power consumption needs, and the length of the cable that governs the loop impedance and voltage drop, i.e. safety and efficiency of the circuit. The latter can be addressed by a larger cable for a given size of circuit, the former only by more or larger circuits.

BTW can anyone tell me how to convert amps into pints?

Now that's a basic question lol, simply divide the customers required load in amps by the cost of a pint multiplied by number required. E.G MAX LOAD =30A cost of pint= £2.50x no reqd = 0.833 pence per Amp/pint

 

[Lucien Nunes]

Sounds like my local has been ripping me off, I will show them your method and see if we can agree on something more like the 0.833p you quote. Going back to the original question, that is one of my arguments against always falling back on the OSG. It discourages people from doing the calcs on the fly. If someone asked me the max circuit length, I'd work it out from the numbers already in my head quicker than I could get the OSG out.