I have a 3kw wall mounted Electric panel heater which is wired into a fused spur box. I would like to move the panel heater 12 feet to another wall. Is ok to purchase longer mains cable and wire one end directly into the heater panel and the other end into the fused spur box?
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112 feet should be okay, just use the right gauge, probably the same gauge as now. Your local government might have something to say about you doing it yourself.– crip659Commented Aug 26, 2022 at 11:25
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1The same gauge wire as is currently in use is probably OK - worth making sure that the wire there is correct for the load and breaker. You're smart enough to ask the question before you start - the previous work may have also been DIY and done by someone who bought whatever was cheap. Very cheap insurance to check the wiring now, just to be sure.– FreeManCommented Aug 26, 2022 at 12:27
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2 Answers
You must be from the UK or some other part of the planet given the terms you are using, (no offense meant, just want to be clear). I've never heard of the term "spur box". Is that what we call in the US a sub-panel?
Next: Glad you are replacing the entire run. Here is the US at 240 v a 3,000 watt heater is considered a "continuous load" and must be de-rated by 20%. Here's the math: 3,000w / 240v = 12.5 amps. 14 ga wire is rated for 15 amps. 15a x 80% = 12 amps. So 14 would be just under what's needed. Depending upon where you are 230v might be more common, which makes the situation worse: 3,000w / 230v = 13.04 amps. De-rating according to US code clearly puts us over the limit for 14 ga. Even if legal, I'd still run 12 ga for less voltage drop and get well into the safety range for your heater.
Again, not knowing where you are means my advice might not be appropriate. I'm only familiar with US NEC code. Maybe some of our "over the pond" folks will chime in.
answered Aug 26, 2022 at 13:46
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A spur is a single connection running off a ring to a separate fused socket [or hard-wired connection]. The US doesn't generally use ring mains, so all your wiring is done on spurs [by UK definition]. I presume the US has a different name for this, but idk what it is, unless it's 'star'. Basically, you buy UK cable 'by the amp' rather than need to know how thick it is. 13A is maximum load, but 15A cable leaves a bit of headroom. btw, in the UK any & all sockets are rated to be safe for this type of heater, but the cable needs to be right, & you're not really supposed to run from an extension.– TetsujinCommented Aug 26, 2022 at 17:02
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The thing about a spur is it needs heavier cable than a ring - because there's no ring to close. Closing the ring just about halves your cable thickness requirement. Running an extra 12' of cable off a spur might be OK, but it really depends how far the spur has already travelled. 15A cable would be best to prevent overheating.
It's 'legal' but only just.
Safest would be to run a new spur from the nearest point on the ring to the new location, or better still - pull the ring round to include it.
For our transpondian friends, here's a simple diagram of a ring + spurs [if not obvious from the drawing, live, neutral & earth all travel this ring together]…
