tails through metal knockouts

maffa ent · Oct 11, 2012

we've replaced a unit, supplied by 16mm swa, and crimped onto swa cores in a large k/o box, then 16mm tails into insulated unit. the tails have been put through separate k/o's out of the k/o box?

is this a big problem, that needs changing?

i realise that they should ideally be through the same hole, but it would be very tight, if not impossible?

thanks in advance!

i=p/u · Oct 11, 2012

With a grommet at least

Mark_Burgess · Oct 11, 2012

Can the small hole be made larger with a cone cutter?

Guest111 · Oct 11, 2012

why not just cut a slot between the holes!

i=p/u · Oct 11, 2012

Sharp edges or magnetising

Thefailsafe2012 · Oct 11, 2012

Or a hacksaw blade?

Engineer54 · Oct 11, 2012

is this a big problem, that needs changing?

I a word ...YES, ...to both parts of this short question!!!

maffa ent · Oct 11, 2012

the job was done when i arrived back at site. of course grommets are fitted! i just don't know whether to get the spark who's fitted it to change it, or just to leave it as is?

a slot may well be an option, although would then introduce ip issues?

i know i've snagged this myself on larger jobs, and have seen some terribly fitted units over the years and called them to high heaven!

is this that bad?

Darkwood · Oct 11, 2012

You can buy stuffing glands up to 50mm quite easily so always the best way to go as it addresses the support issue of the cable joint too, are we to assume its a metal adapter box as you really haven't confirmed that but if it is then yes all phases and neutral should go through a common hole, eddie currents between the holes can generate alot of heat ive seen it melt cables into one sticky pvc mess.

Engineer54 · Oct 11, 2012

maffa ent said:
the job was done when i arrived back at site. of course grommets are fitted! i just don't know whether to get the spark who's fitted it to change it, or just to leave it as is?

a slot may well be an option, although would then introduce ip issues?

i know i've snagged this myself on larger jobs, and have seen some terribly fitted units over the years and called them to high heaven!

is this that bad?

Use Tony's method, and fill slot between knock-outs with an Epoxy Resin to seal it. Now if only grommets are being used at the moment around the knock-outs, i would imagine you already have an IP problem!! lol!!!

tigerpaul · Oct 11, 2012

Slot it, grommet strip and epoxy resin.

loop3 · Oct 11, 2012

Eddy currents. That's the issue when going through metal containment. Basically, same hole.

maffa ent · Oct 11, 2012

thanks all! i get the picture, and will get the spark to make the 2 holes into 1, then make good excess 'hole'.

currently, tails pass through 2x 20mm blind grommets, so the only issue is the eddy currents - i have never seen the effects of this, although i'm quite happy to take your collective word for it!

ta

jeremy · Oct 11, 2012

Just out of interest, does the slot need to be the same width as the holes diameter?, or could it be eg 1/2 the size to enable grommets, or 2 compression glands to still be used?

jeremy · Oct 11, 2012

If thats a stupid question, I'm just thinking out loud!

Guest111 · Oct 11, 2012

jeremy said:
Just out of interest, does the slot need to be the same width as the slots diameter?, or could it be eg 1/2 the size to enable grommets, or 2 compression glands to still be used?

the width of a saw blade will do still stops eddy currents

Knobhead · Oct 11, 2012

maffa ent said:
the job was done when i arrived back at site. of course grommets are fitted! i just don't know whether to get the spark who's fitted it to change it, or just to leave it as is?

a slot may well be an option, although would then introduce ip issues?

i know i've snagged this myself on larger jobs, and have seen some terribly fitted units over the years and called them to high heaven!

is this that bad?

A slot isn't an option it's a must.
Have a look at this

View attachment 15149

if you leave it as it is you're heading for problems with Eddy Currents

View attachment 15150

Bobster · Oct 11, 2012

phil d said:
the width of a saw blade will do still stops eddy currents

Width of the slot to equal plate thickness

Adam · Oct 11, 2012

jeremy said:
Just out of interest, does the slot need to be the same width as the holes diameter?, or could it be eg 1/2 the size to enable grommets, or 2 compression glands to still be used?

Hacksaw blade width should be fine, and allow glands / grommets to still be used.

EDIT:

Alot happens whilst posting a quick reply.

mechelec · Oct 11, 2012

Cut rectangular hole big enough for 4 stuffing glands out of the top of the KO box and make a paxolin gland plate. No sealing between slots, no eddy currents and if done well will look professional.

johnboy6083 · Oct 11, 2012

this is a method ive used several times in the past, and it looks spot on when done properly.

maffa ent · Oct 13, 2012

25 mm hole cut, both tails through same one, other one blanked off, everyone's happy! thanks all

i=p/u · Oct 15, 2012

do you remember the solinoid device the teacher showed , used as an example in level 2 , eddie currents , the rod was roasting hot in 10 seconds

Knobhead · Oct 15, 2012

That was an induction coil i=p/u, exactly the same effect.

This is a good use for induction, the centre of this coil has water pumped through it to keep it cool. Inside the surrounding box is a ceramic channel full of molten iron.

View attachment 15227