Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Replies 14 replies
  • Subscribers 37 subscribers
  • Views 1137 views
  • Users 0 members are here
Options
You may also be interested in

Rules on Spurs

Airconditioningman

Sorry in advance if this is a silly question, but I’m having a few issues with the electrics on an Air Conditioning install in England. The installation is on a domestic property and the house is very large which means that it’s incredibly impractical to run a new cable as the architects made sure to use all available space as living space so there are no voids or attics that can help us.

My question is, what is the maximum amount of power that we can take from  ring main that has no existing spurs on it please. I know we can have a 13a fused spur, but is there any way to get more than 13a without adding a new circuit please? The electrician is saying that 13a is the maximum, but I always thought that t was a little more. 

Parents
  • 0

    The electrician is saying that 13a is the maximum, but I always thought that t was a little more. 

    If you go back far enough (e.g. 15th Ed appendix 5) - the rule for for permanently connected equipment fed from a ring was a max 13A fuse or a max 16A circuit breaker - which is perhaps where your thought hails from. In later editions the rules for rings became less prescriptive (more rules of thumb than absolute regulations) and the 16A option wasn't mentioned any more.

    There is more emphasis these days on ensuring that the (20A) cable of each leg isn't going to be seriously overloaded (whether by total load, or loads not well balanced around the ring, allowing the short leg to carry an overload while the longer leg remains underutilized) - perhaps including during unusual but foreseeable usage (e.g. how many fan heaters would likely be plugged in (and for how long) if the gas boiler went on the blink?).

    So I'd suggest a 16A MCB is still an option - but as a designer the emphasis would be on you to show it would be satisfactory in that particular situation as you wouldn't be able to just rely on the traditional rules of thumb.

       - Andy.

Reply
  • 0

    The electrician is saying that 13a is the maximum, but I always thought that t was a little more. 

    If you go back far enough (e.g. 15th Ed appendix 5) - the rule for for permanently connected equipment fed from a ring was a max 13A fuse or a max 16A circuit breaker - which is perhaps where your thought hails from. In later editions the rules for rings became less prescriptive (more rules of thumb than absolute regulations) and the 16A option wasn't mentioned any more.

    There is more emphasis these days on ensuring that the (20A) cable of each leg isn't going to be seriously overloaded (whether by total load, or loads not well balanced around the ring, allowing the short leg to carry an overload while the longer leg remains underutilized) - perhaps including during unusual but foreseeable usage (e.g. how many fan heaters would likely be plugged in (and for how long) if the gas boiler went on the blink?).

    So I'd suggest a 16A MCB is still an option - but as a designer the emphasis would be on you to show it would be satisfactory in that particular situation as you wouldn't be able to just rely on the traditional rules of thumb.

       - Andy.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines