Bad Electrickery

Terminating onto the sheath of the cable can be extremely destructive- the device can function when re-powered, but the poor quality connection will eventually start arcing and overheat. It can lead to problems like: What Happens When You Terminate On The Insulation

I’m a huge fan of Prysmain/Pirelli’s FP-200. It gets used for a lot of electrical work, especially in fire alarm installation, because it is easy to strip and terminate, can take a bit of a bashing and offers fire resilience.

However, just because it’s flexible doesn’t mean it should end up in a knot.

522.8.3 –  “The radius of every bend in a wiring system shall be such that conductors or cables do not suffer damage and terminals are not stressed.” ‘Other Mechanical Stresses’ in BS7671: 17th Edition.

This can be caused by poor installation, poor fixing, or some other problem that leads to the cable ending up out of shape.

The bend radius of fixed FP-200 Gold is listed as r=6D, where D is the diameter of the cable. So, if we’re using 1.5mm two core & earth for a fire alarm system, the diameter of the cable is 8.1mm. (Source)

This means that your 90 degree turn should complete in just under 5cm, and if you were doing a u-turn, you’d need 2r=97.2mm, just short of 10cm.

Visual inspection of the cable should make it obvious if  the turn is too harsh- the sheath of FP-200 goes white under stress, and once it has been bent, will not straighten out without leaving a kink.

So these bends are probably too tight.

Part 2 to follow soon!

Before:

After:

Sometimes you find something that is in such a tangle, the best thing to is spend a moment fixing it down and rewiring it.

Found in a new building. A little worrying…

You spy some random cables strung behind a fridge, disappearing into trunking. Suddenly full of suspicion, you pull back the toaster to reveal…

An exposed connector block. Cables just coming out of the wall.

All of this should be safely encased in trunking, not in a position where if someone spilled water on the unit they’d have to worry about it becoming live.

Well, I guess that’s one way to do it. Not the right way, mind, but one way.