Spurs off Spurs on radial circuit

[stratplus]

So you can spur off Spurs on a radial socket circuit, is this because the cable is protected via a 20amp breaker at the board compared to 32amp on a ring?

 

[Octopus]

What do you think? Similar to many lighting circuits!

 

[Andy78]

So you can spur off Spurs on a radial socket circuit, is this because the cable is protected via a 20amp breaker at the board compared to 32amp on a ring?

Think about the current carrying capacity of the cable. Are you a trainee ?

 

[stratplus]

Think about the current carrying capacity of the cable. Are you a trainee ?

I am a trainee yes Andy.
Been trying to get my head round rings/Spurs and radials/Spurs. I can understand if you spur off a ring that piece of cable can take potentially 26amps (two 13amp fuses). Now if you spur off that spur your current could be 52amps so overloading the cable.
Finding it difficult to understand how with a radial you can spur off spurs without overloading the cable.

 

[Pete999]

I am a trainee yes Andy.
Been trying to get my head round rings/Spurs and radials/Spurs. I can understand if you spur off a ring that piece of cable can take potentially 26amps (two 13amp fuses). Now if you spur off that spur your current could be 52amps so overloading the cable.
Finding it difficult to understand how with a radial you can spur off spurs without overloading the cable.

Radials usually covered by a 20amp breaker, cant see by extending the radial how you would overload the cable Appendix 15 BYB

 

[Andy78]

I am a trainee yes Andy.
Been trying to get my head round rings/Spurs and radials/Spurs. I can understand if you spur off a ring that piece of cable can take potentially 26amps (two 13amp fuses). Now if you spur off that spur your current could be 52amps so overloading the cable.
Finding it difficult to understand how with a radial you can spur off spurs without overloading the cable.

Well you said it yourself in your opening post. The OCPD is 20A which is less than the CCC of the cable. With a ring circuit the standard OCPD is 32A which is higher than the CCC of the cable in that leg and therefore the potential loading must not exceed that of the CCC of the cable.

See appx 4 for cable calculation procedure and appx 15 for standard circuit arrangements as your revision points for this.

 

[stratplus]

Radials usually covered by a 20amp breaker, cant see by extending the radial how you would overload the cable Appendix 15 BYB

Pete what do you mean by "can't see by extend"?

 

[stratplus]

Well you said it yourself in your opening post. The OCPD is 20A which is less than the CCC of the cable. With a ring circuit the standard OCPD is 32A which is higher than the CCC of the cable in that leg and therefore the potential loading must not exceed that of the CCC of the cable.

See appx 4 for cable calculation procedure and appx 15 for standard circuit arrangements as your revision points for this.

Ok, thank you Andy. Got it now. Every time I read and think I understand something, I read something else and have another ten questions! Read the same four pages for 2 months to understand lighting circuits!

 

[Pete999]

Pete what do you mean by "can't see by extend"?

If you are adding a new socket to a radial you are either extending the circuit, I'll clarify, by extending the radial, I assume you are adding a socket from the last point on the radial.
Read Appendix 15 BYB and get back to us if you don't understand anything.

 

[Paul.M]

Before spurring from a RFC or a radial you must work out what is on that circuit now, what will be on it afterwards and can the cable/protective device provide adequate distribution and protection?

 

[stratplus]

If you are adding a new socket to a radial you are either extending the circuit, I'll clarify, by extending the radial, I assume you are adding a socket from the last point on the radial.
Read Appendix 15 BYB and get back to us if you don't understand anything.

Hi Pete, not doing any electrical work just trying to understand the circuits.
Ok I understand that if you are adding a socket to the end of a radial you are extending. I was more thinking about a spur from a socket so you'd already have two cables in there, spurring would be adding a third cable.

 

[Andy78]

There is a dedicated trainee forum here that you could join if you are in training.

 

[Pete999]

Hi Pete, not doing any electrical work just trying to understand the circuits.
Ok I understand that if you are adding a socket to the end of a radial you are extending. I was more thinking about a spur from a socket so you'd already have two cables in there, spurring would be adding a third cable.

Nothing wrong with that, have you had a look at the BYB yet?

 

[stratplus]

Nothing wrong with that, have you had a look at the BYB yet?

I don't have the yellow book (apart from osg) but I do have the red one. I'll have a look now.

 

[Pete999]

I don't have the yellow book (apart from osg) but I do have the red one. I'll have a look now.

Not sure which Appendix it is in the BRB probably the same as the latest book