|Mike Donnerstag||16/05/2021 16:57:40|
201 forum posts
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.
Thanks in anticipation,
|697 forum posts|
Just bought a surface architrave box with a blank lid - Crabtree - for a simiar job
Might be worth investigating
|David George 1||16/05/2021 17:22:51|
1629 forum posts
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.
|Nicholas Farr||16/05/2021 18:15:19|
2945 forum posts
Hi, I would probably do the same sort of thing that Bill and David have said.
|Robert Atkinson 2||16/05/2021 18:24:24|
1072 forum posts
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.
|Martin Kyte||16/05/2021 18:30:42|
2525 forum posts
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.
|Martin W||16/05/2021 19:20:21|
|894 forum posts|
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
|2146 forum posts|
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.
|Robert Atkinson 2||17/05/2021 09:33:54|
1072 forum posts
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.
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.
This thing needs work before it is plugged in. it should NOT be used as is. That is my professional opinion.
4660 forum posts
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
2224 forum posts
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.
|Martin Kyte||19/05/2021 12:16:28|
2525 forum posts
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.
|Ian P||19/05/2021 13:36:45|
2512 forum posts
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.
|Robert Atkinson 2||19/05/2021 17:59:12|
1072 forum posts
Screw terninal connectors are OK INSIDE control panels, they are not OK wher the user can touch them.
What ate your views on frayed insilaton and wires rubbing agianst and trpped under the raw edges of brass sheet?
|Mike Donnerstag||19/05/2021 18:19:28|
201 forum posts
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,
|David George 1||19/05/2021 18:55:54|
1629 forum posts
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.
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