Strand (and Furse) Pattern 23 mirror spot refurbishment

Sooner or later, most theatres will be faced with PAT (Portable Appliance Testing).  Although this is meant to ensure electrical equipment is up to scratch (obviously a Good Thing), as with many Health and Safety issues, a load of myth and bulls**t has also crept in.  Some independent PAT testers might insist on older equipment having niceties like earth bonding and OTT cable clamping.  Although such equipment might be perfectly safe, it was never designed with this in mind since no requirement existed at the time of manufacture.

LADS (Ledbury Amateur Dramatic Society) had this problem with a few of our stage lights.  In some cases, this was a good time to consign items past their use-by date to the skip and get something more modern.  (Before we did, we stripped them of anything useful to keep as spares.)  However, the Strand Pattern 23 Mirror Spot (and the Furse copy), of which we have six, are simply too useful to throw away, even if they are approaching 50 years old.  They were quite advanced when they first hit the stage: die-cast body (when everything else was heavy steel) and remarkably efficient optics.

Although the 23's cable clamping left a bit to be desired, simply pulling a zip-tie tight round the cable just inside the entry hole was sufficient to stop it pulling through - this arrangement was fine for years but it wasn't good enough for our PAT man.  Also, 23's don't have 'cross-bonding', which in simple terms is internal earthing connections between all exposed metal parts, so earth continuity doesn't rely on hinges etc. to make good electrical contact (as if you'd ever fire up a lantern with the door open - and when it's locked shut the locking screw ensures a good contact anyhow)....  Most spots and Fresnels have a movable lamp carrier, which also needs to be bonded to be really Kosher.  The following tells you how to future-proof a 23.

There isn't much space inside a 23, so devising a clamping arrangement that would keep our PAT man happy was a bit challenging.  We didn't use proprietary cable clamps since most of them are too big - and plastic ones would probably melt.  Most of our lanterns were fitted with immersion heater cable, which is far too thick.  23's run very hot, so the cable must be a 'hot' type - we bought a 25m drum of a silicone insulated type from RS Components (part no.1927934) for this and future repairs.

Other items needed to do this job are:

Both RS and Farnell supply all these bits, but they were cheapest (at the time of writing) as shown above.

Procedure

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Steve Glennie-Smith
Last updated Feb 4th 2010.