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Help with Electrics on a Bow Bending Iron

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Mike Donnerstag16/05/2021 16:57:40
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201 forum posts
45 photos

I recently acquired a large iron for pre-bending musical instrument bows. The tool consists of two large aluminium blocks in which several heating elements are inserted. These are wired (using their own heat resistant wires) to ceramic connectors/terminal blocks which in turn are connected to a thick flex and a 13A plug.

While the metal parts on the tool are well earthed, the fact that much of the electrics is exposed worries me, particularly the exposed screws on the terminal blocks.

I wondered whether there are any electricians amongst you who could advise on the best way to make the electrics safer and less exposed. Obviously any solution would need to be heat-resistant.

img_1590.jpg

Thanks in anticipation,

Mike

br16/05/2021 17:12:30
697 forum posts
3 photos

Just bought a surface architrave box with a blank lid - Crabtree - for a simiar job

Might be worth investigating

bill

David George 116/05/2021 17:22:51
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1629 forum posts
492 photos

I have made tooling with similar heaters and I would mount these ceramic heaters inside an aluminium channel with a lid and a metal grommet for the heat resistant flex.

David

Nicholas Farr16/05/2021 18:15:19
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2945 forum posts
1333 photos

Hi, I would probably do the same sort of thing that Bill and David have said.

Regards Nick.

Robert Atkinson 216/05/2021 18:24:24
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1072 forum posts
20 photos
Posted by Mike Donnerstag on 16/05/2021 16:57:40:

I recently acquired a large iron for pre-bending musical instrument bows. The tool consists of two large aluminium blocks in which several heating elements are inserted. These are wired (using their own heat resistant wires) to ceramic connectors/terminal blocks which in turn are connected to a thick flex and a 13A plug.

While the metal parts on the tool are well earthed, the fact that much of the electrics is exposed worries me, particularly the exposed screws on the terminal blocks.

I wondered whether there are any electricians amongst you who could advise on the best way to make the electrics safer and less exposed. Obviously any solution would need to be heat-resistant.

img_1590.jpg

Thanks in anticipation,

Mike

Hi Mike, The construction of that is clearly not acceptable. in adition to what you have spotted there are bare metal saddles used for cable clamps.
The wiring needs to be enclosed in a heatproof cover with the flexes replaced by heat reaistant types with correct cable glands. It should also have overheat potection. If you are business, even a sole trader, health and safety law requires that electrical equipmnt is safe.
I'd be happy to help you with this. I'm in Cambridgeshire so not that far away. You can send me a PM.

Robert G8RPI.

Martin Kyte16/05/2021 18:30:42
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2525 forum posts
45 photos

They look more scary than they are actually. You would need to try really hard to to come into contact with those terminals. Certainly you cannot get your fingers on the screws as they are sub flush and in quite small recesses. In fact when used with a working RCCB I would say that the bigest hazard is burning your fingers. However do feel free to add a metal box or a simple shield if it makes you feel safer.

How are they actually used.? If it's the case that everything is assembled and cramped up then the current is switched on just a good operating proceedure will keep you safe.

regrds Martin

Martin W16/05/2021 19:20:21
894 forum posts
29 photos

I would have thought that the risk is minimum as all the terminal blocks that can be seen in the photo are marked 'N' and the live wires appear to be terminated in screened finger proof enclosures. It only becomes dangerous if some muppet wires up the mains three pin plug incorrectly.

Many of us live with and use bog standard toasters where the live mains is easily accessed with metal objects i.e. cutlery, skewers, etc. all of which are readily to hand and make tempting tools, especially for little hands, for prodding/poking the internal workings of said item. How many of us actually think that when these devices are working that parts of the bare metal element are actually at mains live potential and relatively easy to access.

Just a thought

Martin

Emgee16/05/2021 20:04:30
2146 forum posts
265 photos

Without seeing a picture of the device in user mode showing the complete assembled heater it is difficult to see any problem, as both Martins have indicated it is not likely you can come to harm if used with care, however if totally enclosed with a heat resistant cover the user would feel happy.
It is not meant to be hand held or even handled in use as no doubt the metal parts get very hot.

Emgee

Robert Atkinson 217/05/2021 09:33:54
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1072 forum posts
20 photos

The condition of thi equipment is NOT acceptable. Apart from the basic design being deficient, there are faults present.

1/ Outer brading on single conductor wirw from heater cartridges damaged in a number of areas.
2/ Edge of brass cover on upper part touching blue wire.
3/ Wire running under edge of lower brass coveer in two places.
4/ Flex grimped at sharp angle under bare metal clamp.
4 Appears to be bare wire strand exposed on one terminal block (lower N)

Not all the terninal blocks are neutral.The connector blocks are not supposed to be used in accessible locations. Earthing is not a subsitute for poor design and construction. There is no way this thing would pass even a a basic user visual inspection never mind a PAT test.

Just being able to see blue and brown insulation on a mains cable is a failure on a basic user visual safety inspection.
Is anyone who is saying this thing is OK to use prepared to stand up at an inquest and defend their statement? Put up their house as a bond for any insurance claim when the OP's house burns down?
I don't think so.

This thing needs work before it is plugged in. it should NOT be used as is. That is my professional opinion.

Robert G8RPI.

Ady117/05/2021 11:07:20
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4660 forum posts
709 photos

I tend to test stuff on the garage rcd circuit

Annoyed me at the time for the cost but it's actually super useful for dodgy old electrics

Even if something powers up ok you can pull it about with a pair of gloves on to test for general integrity in use

Had to rewire some of an old drummond M I got, which ran fine when I picked it up

Steviegtr17/05/2021 22:56:26
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2224 forum posts
311 photos

When doing inspection & testing on control panels etc. We had the British standard finger to test with. It was i think a piece of 10 or 12mm nylon rod. You poked around inside the panel. If you could make electrical contact with anything using the finger it was a fail. That was back in 16th edition so not sure what they use now. Ceramic connectors were always used for heating elements & are quite safe.

By all means enclose if you like but that sometimes raises the temperature that you do not want. If i ain't broke.

Steve.

Martin Kyte19/05/2021 12:16:28
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2525 forum posts
45 photos

Interestingly I have just done a PID heater controller for work an aspect of which may be of use in this context. It is a heater block for the buissness end of a microtome for slicing fly brains.

The original, made eleswhere, used 240V heaters which I swapped for 110V versions with the same power rating. These were driven from a 110V transformer centre tapped to ground ensuring that the heaters were limited to 55V ac at each end and switched via an SSR

If 110V heaters could be obtaines for the Bow bender the unit could be rewired accordingly and powered from a standard 110V site transformer.

regards Martin

Ian P19/05/2021 13:36:45
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2512 forum posts
102 photos

I absolutely 100% endorse what Robert Atkinson-2 wrote above!

More information about the equipment itself would help us suggest how it could be made safe to use, questions that occur to me include,

What temperature does it operate at?

Is it temperature controlled?

If so, do each of the ali blocks each have their own temp sensor?

Are the two block held in some mechanical jig, hinged frame etc, or do they just bolt together in use?

Whilst the wiring and accessory bits visible are designed to be heat resisting, we can also see nylon cable ties which do not seem to have been melted/overheated, so maybe the operating temperature is no so high?

Fastening terminal blocks or other parts to a plate on short standoff spacers would greatly reduce their temperature and probably make assembly and wiring easier and be something perforated protective enclosures could be attached to.

It does not look like this equipment is a commercial product as it certainly should not be on the market as it is. I have in the come across products with mains cables with just a knot and grommet (and choc-block) terminals stuck down with hot-melt glue. Nowadays fortunately we have better regulations, CE and other certifications.

Ian P

Robert Atkinson 219/05/2021 17:59:12
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1072 forum posts
20 photos

Steve,

Screw terninal connectors are OK INSIDE control panels, they are not OK wher the user can touch them.
They should also be secured.

What ate your views on frayed insilaton and wires rubbing agianst and trpped under the raw edges of brass sheet?
We have been around this buoy before. The requirements for fixed industrial installations (control panels) are not the same as portable electrical equipment regulations. The bow heater IS broken.

Robert G8RPI.

Mike Donnerstag19/05/2021 18:19:28
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201 forum posts
45 photos

Many thanks for all of the information. All of your comments will be taken into account.

The iron is not a commercial product. There are frankly too few bowmakers to make such a product worthwhile developing. The metal covers conceal thermostats, limiting the temperature.

I will check to ensure the iron is functional and make some changes to improve its safety based on all of your comments.

Once again, many thanks to all,

Mike

David George 119/05/2021 18:55:54
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1629 forum posts
492 photos

Hi Mike if you want any heat proof sleeving, cable, tape, etc I can drop some in the post. Just drop me a message where to send to. It is spare stuff I have left over from thus type if work.

David

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