Published:
14 September 2010
Category:
Q&A
Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning fuse protection on a final ring circuit, is answered by SELECT:
Question: Is it permissible to downrate a BS88 32A fuse to a BS88 25A fuse on a ring final circuit?
The reason for thinking of doing this is because in a recent fixed wiring test, the maximum Zs measured was 0.98ohms and the maximum allowed on a 32A fuse is 0.83ohms, and where a BS88 25A fuse is 1.15ohms.
Note that an RCD on this circuit would be impracticable.
Answer: Yes you could change the protective device from a 32A to a 25A to comply with the temperature corrected values of Zs however the maximum loading of the circuit should be considered to ensure this is suitable.
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