Tightening Terminals on CU's

[murphy4869]

What are thoughts on checking the tightness of terminals inside a CU. Do you pros do/recommend doing this on a regular basis?

Only ask as I work for one of the emergency services attended a fire at a horse stables which initally was deemed suspicious but was traced, (by fire investigation team) to a loose connection from the SWA into the CU of the stables I think neutral side.

Complete devestation as it was a timber building nothing left of it-luckily no horses in there at the time.
Got me thinking though!!!!

 

[NotHimAgain]

Checking that terminals remain 'tight' should be part of the inspection or maintenance process.

However, this should be carried out with care. Over tightening can damage the terminal. Repeated tightening of brass tunnel terminals on every planned maintenance visit is a common cause of conductors being cut through.

Most electricians eventually come with a built in torque wrench . They generally develop the skill of tightening a terminal just to the point at which further force would cause damage. BT used to issue a small torque limiting driver for screws and small nuts.

 

[kai]

I re-tighten the Clamp type terminals on my Wylex CU every couple of years - just to be on the safe side.

 

[Paul_C]

I can't help thinking that a lot of loose connections these days are caused by the lousy "Use any type screwdriver you have" heads on the terminal screws, but which in reality don't really offer a snug, tight fit to any of them.

Why manufacturers continue to think that these atrocities are better than just using a good slotted or Philips head is a mystery.

 

[timtheenchanter]

Universal=one size fits nowt

 

[ColJack]

you don't need a snug fit..
if it's got a slot, then stick the biggest slotted driver in that will fit and crank it down..

if you apply too much pressure you'll do one of 2 things, cam out the head, or break the screwdriver

 

[GaryMo]

I've never had a problem using a larger slotted screwdriver.

 

[kai]

On the old Wylex fuseboard which I ripped out, each terminal has two big slotted terminal screws on every connection - no wonder loose connections were less of a problem in the olden days - as long as the units were properly installed of course.

 

[GaryMo]

Loose connections shouldn't be less of a problem in the past compared to nowadays if the correct tool is used and the person using it is competant to do so.

 

[mfarrow]

Most screw heads on these 'combined' screws are slotted or Pozidriv[e], not Philips.

Using a Philips screwdriver in a Pozidriv head will cause it to cam out. Otherwise I've had no problem with them.

 

[333rocky333]

Regardless of the tightness of the screws.
More loose connections I find are due to the way the wire enters the sometimes oversize hole.
The cable can often be found down the sides of the screws,
Only this week I found a blue phase 100 amp supply with a lot of copper showing above the terminal.
On investigation the screw was still tight, but the cable had popped out.

However CU's these days, they smoke and smell a bit but rarely catch fire I would have thought.

 

[plugwash]

I do wonder if there was some other factor in the barn fire, e.g. some material that catches fire easily very close to (or even inside..........) the overheating CU.

Modern CU plastics have flame retardants incorporated so they won't support a flame.

 

[flameport]

The 'combined' screws on MCBs and suchlike should be tightened with the tool designed for the job:
http://www.dm-tools.co.uk/product.php/section//sn/WER073601
This avoids any problems of damaged screws or loose terminals.

 

[RF Lighting]

No good for a wylex fuse board though

They vary between combination phillips and pozi on the same model of MCB, and I still find I can get screws tighter with a decent flat head screwdriver than those combination ones.

 

[Paul_C]

Most screw heads on these 'combined' screws are slotted or Pozidriv[e], not Philips.

True, many are slotted/Pozi rather than slotted/Philips, but the same principle applies.

I think the fact that at least one manufacturer now makes a special screwdriver designed specifically for these combination heads rather proves the point.

But why do so many equipment manufacturers insist on using these horrible screws anyway? Do they really think that the people working with them aren't going to have a range of slotted, Philips, and Pozi screwdrivers?