Earthing a cast iron pipe man light

[Kentish Man]

I have constructed a cast iron pipe man figure ( steam punk type ) using a small spotlight with on/off switch on the lead then to the plug. Need to cut the lead and extend this to fit through the cast iron pipe ( between on/off switch and the light unit ). Cable is only two wires Blue/Brown no earth. Is this okay for using on the figure or should it have an earth cable and if so where would this be attached to the figure.

Thanks in advance

 

[Lucien Nunes]

It depends on whether the insulation and mechanical support you provide for where the cable runs through the metal body and the reamining parts of the original lamp meets the requirements for Class II, in which case that is preferable. If not, it will have to meet the requirements for Class I and be suitably earthed. Do you have sight of the applicable standards that it should comply with?

 

[pc1966]

For a DIY style of project trying to establish fully double insulated construction (and all parts used) is unlikely to be practical, so yes you should earth the metalwork for protection.

In that case you should be using 3-core wire and have it attached somewhere to the metalwork. Assuming the whole thing is reasonably well fixed together (i.e. welded or bolted) you need only attach to one point.

Usually you would have some form of cable clamp to take any mechanical strain off the cable run as the cable enters the structure, and if that has some fixing screws to the metalwork you can probably use a ring-terminal crimped or soldered to the earth wire there.

 

[pc1966]

Just to add that obviously a protective earth connection has to be reliable, so you need to (a) properly connect the wire to the terminal, and (b) make sure the terminal stays in contact with the metalwork.

For crimp terminal please, PLEASE, get a ratchet tool and not those horrible plier things in kits from Halfords, etc. This would be my minimum cost option:

Expert Ratchet Crimper | Toolstation

Precision ratchet, crimps red 0.5-1.5mm, blue 1.5-2.5mm and yellow 4-6mm.

www.toolstation.com

But if you plan a lot of work that might need it, this is a professional tool that does a better job and will do so for decades:

RS PRO Ratcheting Hand Crimping Tool for Terminal | RS Components

uk.rs-online.com

This is typically what you would use with a M4 screw (or similar) and is fine for the sort of cable range you would be using (typically 0.75mm^2 3-core cable and a 3A fuse, etc):

Ring Lug Connectors

www.toolstation.com

To make sure the terminal does not come away from the metalwork use some form of locking, for example star or spring washers if the screw is tapped in to the metal work, or a nylock nut, etc, on the end of a bolt passing through it.

 

[Kentish Man]

Just to add that obviously a protective earth connection has to be reliable, so you need to (a) properly connect the wire to the terminal, and (b) make sure the terminal stays in contact with the metalwork.

For crimp terminal please, PLEASE, get a ratchet tool and not those horrible plier things in kits from Halfords, etc. This would be my minimum cost option:

Expert Ratchet Crimper | Toolstation

Precision ratchet, crimps red 0.5-1.5mm, blue 1.5-2.5mm and yellow 4-6mm.

www.toolstation.com

But if you plan a lot of work that might need it, this is a professional tool that does a better job and will do so for decades:

RS PRO Ratcheting Hand Crimping Tool for Terminal | RS Components

uk.rs-online.com

This is typically what you would use with a M4 screw (or similar) and is fine for the sort of cable range you would be using (typically 0.75mm^2 3-core cable and a 3A fuse, etc):

Ring Lug Connectors

www.toolstation.com

To make sure the terminal does not come away from the metalwork use some form of locking, for example star or spring washers if the screw is tapped in to the metal work, or a nylock nut, etc, on the end of a bolt passing through it.

Thank you very much for the information. Have ordered the RS Pro crimping tool today. Enclosed is a picture of the type of light it will be. Also the type of power cord I was thinking of using. My idea is to run the power cord through a hole drilled in the back of the 45 degree bend (marked in red) and join this up to the wires coming down from the light. The green box shows the tee junction and I was planning to drill up through the bottom of this connector (3rd Pic ) and attach the earth wire to the inside of the connector with a nut/washer/bolt once crimped up. This way the bolt head will be on the outside bottom of the pipe and out of sight and the connection will be out of sight inside the fitting when all the metal parts are screwed together. I presume this would be okay for this type of light?

 

[Kentish Man]

It depends on whether the insulation and mechanical support you provide for where the cable runs through the metal body and the reamining parts of the original lamp meets the requirements for Class II, in which case that is preferable. If not, it will have to meet the requirements for Class I and be suitably earthed. Do you have sight of the applicable standards that it should comply with?

Thank you for your reply. I have enclosed pictures of the type of light and cord I was planning to use. Entry for the cord I was hoping to run via a hole drilled into the back of the 45 degree joint and connecting up to the light. Drilling a hole in the bottom of the Tee joint and connecting the earth wire by Bolt/washer/nut inside. This way the bolt head will be at the bottom of the light out of sight and the earth connection will be inside the Tee joint out of sight when all the metal parts are screwed together. Hope this explains it more clearly.

 

[pc1966]

My idea is to run the power cord through a hole drilled in the back of the 45 degree bend (marked in red) and join this up to the wires coming down from the light. The green box shows the tee junction and I was planning to drill up through the bottom of this connector (3rd Pic ) and attach the earth wire to the inside of the connector with a nut/washer/bolt once crimped up.

Where the cable goes in needs to have some form of protection against chaffing against the drilled hole, and really some form of restraint.

If you can fit a gland like one of these (assuming your cable is no more than 6.5mm outer diameter, otherwise the larger sizes such as PG9/M16 would be needed)) you achieve both:

RS PRO Metallic Nickel Plated Brass Cable Gland, M12 Thread, 3mm Min, 6.5mm Max, IP68 | RS

uk.rs-online.com

However I don't know how it compares in terms of size - your light looks a bit smaller than I originally thought when you talked of cast pipe and that particular gland is for a 12mm hole. Either flat-ish sheet using the supplied nut, or a tapped (threaded) hole, though that might not be so easy on a strong curve.

It is quite possible you could fit a (probably larger) gland to one of the hands or feet if it matched the thread size and would make installation easier, but may go against your aesthetics!

You also get plastic glands that are cheaper and in white/grey/black/red choices.

Or you could look at a grommet for cable entry and some sort of clamp ore P-clip arrangement internally to the pipe, that is typical of many commercial product (think of how the cable is held in your typical rewirable 13A plug).

This way the bolt head will be on the outside bottom of the pipe and out of sight and the connection will be out of sight inside the fitting when all the metal parts are screwed together. I presume this would be okay for this type of light?

Yes, it sounds fine. You can also join the wires internally using crimp insulated "butt joints" if needed, but they are permanent (short of cutting wire and stripping for another go), for example:

Butt Connectors

www.toolstation.com

Or the better though larger approach are the spring-loaded Wago terminals or other brands such as these:

In Line Spring Lever Connectors

Use these 32A spring lever connectors for an easy, fast-fit connection. The levers are a real time-saver, and the compact design makes them easier to work with in confined spaces.• 2 in 2 out inline lever connectors• Spring levers for easy, fast-fit connections• Colour-coded for live and...

www.toolstation.com

(though again I don't know if it fits your tube size easily enough and unfortunately Toolstation are rubbish at providing measurements, etc, on the web site).

 

[pc1966]

This data sheet has the RS metal glands' dimensions, but many many others are available:

https://docs.rs-online.com/0e45/0900766b814183a0.pdf

 

[Lucien Nunes]

How about replacing the 135° elbow at the back with a Y-junction so that there is dedicated branch to serve as an entry point for the flex. Into the new branch fit a blanking plug drilled and tapped for the compression gland. Not all glands are equal as far as flex retention and resistance to unscrewing. I prefer the Lapp Skintop range, they are a little more expensive but particularly effective at retaining the cable.

When separating the cores inside the tube, leave plenty of surplus on the earth. If the flex does get tugged out, e.g. if the lamp falls off the shelf and snatches at the flex with its full weight and momentum, you want the earth to remain connected even while the line and neutral rip out of the lampholder. In this sort of scenario it is likely someone will make a dive for the lamp to catch it and if the line contacts the tube after the earth has parted company they will be tightly grasping a fully live metal object.

 

[Kentish Man]

Where the cable goes in needs to have some form of protection against chaffing against the drilled hole, and really some form of restraint.

If you can fit a gland like one of these (assuming your cable is no more than 6.5mm outer diameter, otherwise the larger sizes such as PG9/M16 would be needed)) you achieve both:

RS PRO Metallic Nickel Plated Brass Cable Gland, M12 Thread, 3mm Min, 6.5mm Max, IP68 | RS

uk.rs-online.com

However I don't know how it compares in terms of size - your light looks a bit smaller than I originally thought when you talked of cast pipe and that particular gland is for a 12mm hole. Either flat-ish sheet using the supplied nut, or a tapped (threaded) hole, though that might not be so easy on a strong curve.

It is quite possible you could fit a (probably larger) gland to one of the hands or feet if it matched the thread size and would make installation easier, but may go against your aesthetics!

You also get plastic glands that are cheaper and in white/grey/black/red choices.

Or you could look at a grommet for cable entry and some sort of clamp ore P-clip arrangement internally to the pipe, that is typical of many commercial product (think of how the cable is held in your typical rewirable 13A plug).


Yes, it sounds fine. You can also join the wires internally using crimp insulated "butt joints" if needed, but they are permanent (short of cutting wire and stripping for another go), for example:

Butt Connectors

www.toolstation.com

Or the better though larger approach are the spring-loaded Wago terminals or other brands such as these:

In Line Spring Lever Connectors

Use these 32A spring lever connectors for an easy, fast-fit connection. The levers are a real time-saver, and the compact design makes them easier to work with in confined spaces.• 2 in 2 out inline lever connectors• Spring levers for easy, fast-fit connections• Colour-coded for live and...

www.toolstation.com

(though again I don't know if it fits your tube size easily enough and unfortunately Toolstation are rubbish at providing measurements, etc, on the web site).

Thank you for the information and links, looking at the cable glands would appear to be a nice way to go and yes this would mean a bit of re-design on the figure. Looking at changing one of the back 90 degree joints on the leg to a Tee joint, this would hopefully give me a place to screw the cable gland into (threads matching of course) and as it would be pointing backwards, just right for the cable, should fit in quite nicely. Will give the wago terminals a look and see if I can find some sizes for them at the moment I think they will be to big to fit inside the pipe but you never know.

 

[Kentish Man]

How about replacing the 135° elbow at the back with a Y-junction so that there is dedicated branch to serve as an entry point for the flex. Into the new branch fit a blanking plug drilled and tapped for the compression gland. Not all glands are equal as far as flex retention and resistance to unscrewing. I prefer the Lapp Skintop range, they are a little more expensive but particularly effective at retaining the cable.

When separating the cores inside the tube, leave plenty of surplus on the earth. If the flex does get tugged out, e.g. if the lamp falls off the shelf and snatches at the flex with its full weight and momentum, you want the earth to remain connected even while the line and neutral rip out of the lampholder. In this sort of scenario it is likely someone will make a dive for the lamp to catch it and if the line contacts the tube after the earth has parted company they will be tightly grasping a fully live metal object.

Thanks for the information, will give the lapp skintop range a look. regarding a place to fit the compression cable gland. I think I could make a change on one of the 90 degree joints at the back on the leg and fit a Tee joint as this would give me the hole to screw a cable gland fitting into it ( screw threads matching ). This would be pointing backwards so would not look out of place for a power cable coming into the light.

Taken on board what you have said about cable surplus thanks

 

[telectrix]

Thank you for your reply. I have enclosed pictures of the type of light and cord I was planning to use. Entry for the cord I was hoping to run via a hole drilled into the back of the 45 degree joint and connecting up to the light. Drilling a hole in the bottom of the Tee joint and connecting the earth wire by Bolt/washer/nut inside. This way the bolt head will be at the bottom of the light out of sight and the earth connection will be inside the Tee joint out of sight when all the metal parts are screwed together. Hope this explains it more clearly.

like it. sort of thing i'd have as a reading lamp as opposed to the fancy tat that 'er indoors favours.

 

[Lucien Nunes]

I like it too. Normally I'd say it was whimsical but the proportions and posture of this chap strike a chord somehow.

The tee idea sounds good. There are cable glands with BSP threads that would screw straight into the tee but they are not widely available, and a gland that fits your pipe might be too large for the flex. Ideally you want the flex to be near the top end of the gland's adjustment range. E.g. a gland rated for 5-8mm cable might clamp best at 7mm. I would choose a Skintop gland with an M12 or M16 thread and adapt to fit the tee socket with something like this:
M16x1.5F x 1/2"BSPM thread adaptor

 

[pc1966]

I was quite surprised by how expensive that adaptor is, though of course it is for real hydraulic work.

Are those fittings the same thread as radiator end caps? If so it might be possible to use something like these and drill it for any gland smaller that suits your cable, etc:

1/2" BSP Brass Plain Blanking Plug

Brass plain blanking plug with 1/2 inch BSP male thread (British Standard Pipe Thread)

www.stevensonplumbing.co.uk

1/2" BSP Brass Blanking Cap / Blank Nut

Brass blanking cap / blank nut with 1/2 inch BSP female thread

www.stevensonplumbing.co.uk

(Just random web site showing them, probably available at plumber's suppliers all over the UK.)

 

[marcuswareham]

Very nice

I had the same conundrum as you with a wall lamp I made using a trombone

I couldn't find a suitable place to attach and earth easily and without affecting the look

So instead I used a SELV transform and a 12v light bulb, depending on your bulb fitting this could be an option for you