What size lug?

[BlueStringPudding]

What size lug would a typical earth cable need in an engine bay? I assume it's measured as M-something?

The cable itself is about 1" diameter if that's any help.

Thanks.

[Chewbacka]

17 minutes ago, BlueStringPudding said:

What size lug would a typical earth cable need in an engine bay? I assume it's measured as M-something?

The cable itself is about 1" diameter if that's any help.

Thanks.

A lug has 2 dimensions of interest.

1). The size of the hole that the cable inserts into.  This is usually quoted in mm2 to match the cable

2). The diameter of the hole in the flat bit that is sized to match the bolt diameter that will bolt it down.  Often m8 or m10.

 

added - you also need to make sure it is crimped onto the cable properly, can’t do it with a hand crimper, ideally use a hydraulic crimped.

 

measure the diameter of the copper cores and this will tell you the mm2

https://www.engineeringtoolbox.com/wire-square-mm-diameter-d_1874.html

Edited August 25, 2019 by Chewbacka

[BlueStringPudding]

Just now, Chewbacka said:

A lug has 2 dimensions of interest.

1). The size of the hole that the cable inserts into.  This is usually quoted in mm2 to match the cable

2). The diameter of the hole in the flat bit that is sized to match the bolt diameter that will bolt it down.  Often m8 or m10.

Thanks. I need to get a whole new fat cable made up. So it's the M8 or M10 bit that sounds like what I need to know.

I assume that if I err on the side of caution and go too large with the lug's bolt diameter, a washer can make a decent connection? Rather than risking going too small.

[WotEver]

4 minutes ago, BlueStringPudding said:

 

I assume that if I err on the side of caution and go too large with the lug's bolt diameter, a washer can make a decent connection? Rather than risking going too small.

That’s not a good assumption. Select your bolt (M8 or M10) and weld/bolt it into place. Now you know what size it is so you can have the correct size lug crimped on. 

[Chewbacka]

6 minutes ago, BlueStringPudding said:

Thanks. I need to get a whole new fat cable made up. So it's the M8 or M10 bit that sounds like what I need to know.

I assume that if I err on the side of caution and go too large with the lug's bolt diameter, a washer can make a decent connection? Rather than risking going too small.

The purists will tell you no, but I have done that and I have also drilled an 8mm to a 10mm hole.

 

but if the bonding stud is already there then measure it, if not then you are free to decide if you want to use m8 or m10.

Edited August 25, 2019 by Chewbacka

[Tony Brooks]

3 minutes ago, BlueStringPudding said:

Thanks. I need to get a whole new fat cable made up. So it's the M8 or M10 bit that sounds like what I need to know.

I assume that if I err on the side of caution and go too large with the lug's bolt diameter, a washer can make a decent connection? Rather than risking going too small.

 

Not the best idea because you really need to clean any paint away from under the lug and using a  washer gives a gap around the bolt for damp and thus rust to get into, but its will almost certainly work well for some time.

[WotEver]

2 minutes ago, Chewbacka said:

The purists will tell you no

Hey, I resemble that remark!

[BlueStringPudding]

15 minutes ago, Chewbacka said:

The purists will tell you no, but I have done that and I have also drilled an 8mm to a 10mm hole.

 

but if the bonding stud is already there then measure it, if not then you are free to decide if you want to use m8 or m10.

Yeah, I've done the drilling thing once before too But It was thinner metal, this lug will need to be meaty. 

 

The damaged lug/cable and the bolt were measured as best as they could be reached at the time, but the measurement is wrong.  There's no way the negative bolt is 80mm in diameter! ? It's a long and fat cable so could be an expensive mistake If I replace it wrongly. The lug came off while the batteries were being replaced and I think it's being held together with gaffer tape at the moment. So I need to replace it soon as, really. I just can't physically get into the engine bay myself so I'm weighing up what my options are with replacing it.

 

I will have to buy the cable already made up. That's what I did before although it's still broken.

16 minutes ago, WotEver said:

That’s not a good assumption. Select your bolt (M8 or M10) and weld/bolt it into place. Now you know what size it is so you can have the correct size lug crimped on. 

The earth bolt is already there. I'm not changing bolts. Just buying a new cable.

Edited August 25, 2019 by BlueStringPudding

[Chewbacka]

Just maybe the bolt was measured as 8.0mm and you missed the dot

[Chewbacka]

You may be able to crimp a new lug onto the existing cable, which would save some money, depending on the condition of the copper strands and if there is a bit of free length if the end needs cleaning up.  A crimp if done correctly doesn’t fall off.

[BlueStringPudding]

I just wrote down what I was told, no decimal points were mentioned - "eighty" sounds very different to "eight point oh." 8mm would make more sense, certainly. Unless the length was accidentally measured instead of the diameter. 

 

I'm now also wondering whether a 1" diameter cable can be correct? That's excluding the sheath because I asked at the time. That's a lot of square millimetres.

 

I think a "Back to the drawing board" situation might be in order.

19 minutes ago, Chewbacka said:

You may be able to crimp a new lug onto the existing cable, which would save some money, depending on the condition of the copper strands and if there is a bit of free length if the end needs cleaning up.  A crimp if done correctly doesn’t fall off.

Yes. I wondered that. But to buy lugs and a huge specialist tool for a one time job seems excessive too. I'll have to ask what the end of the cable looks like. I didn't see it myself.  It seems that whomever I bought the ready-made cables off didn't crimp it on properly originally.

 

Edited to add: apparently the cable end is in good nick and the lug appeared only pushed on not crimped in the first place! That's a bit of a concern. Hope it's just one that got missed and that the rest aren't like that coz I bought the cables all from the same supplier some time ago and they've been holding my Gibbo'd wiring together ever since ?

 

Anyway, I might not need to buy a whole new cable. All I need is a roving giant crimpulating person with a sign that says: "WILL CRIMP FOR BEER" 

Edited August 25, 2019 by BlueStringPudding

[BEngo]

If it will survive as is until I pick up the MPPT widget I will pack my big crimping tool and do it for you then.

The crimp tool goes up to 50 sq mm cable.

Can you get close enough to take a snap of the lug and cable?  We may well be able to ID the lug and cable size from a pic.

 

N

[tree monkey]

1 minute ago, BEngo said:

If it will survive as is until I pick up the MPPT widget I will pack my big crimping tool and do it for you then.

The crimp tool goes up to 50 sq mm cable.

Can you get close enough to take a snap of the lug and cable?  We may well be able to ID the lug and cable size from a pic.

 

N

It should survive, tbh it doesn't look like it was crimped in the first place and sorry for the poor measurements, I was basically a puddle of liquefied monkey down the engine hole, trying to fit 4 new batteries.  I guess it was approximately 3,000'c down there today

[Chewbacka]

Just thinking some more, and people when talking cable size will sometimes (being sloppy) miss off the ‘square’ so a cable described as 25mm maybe is a 25mm2 cable, though it would not be described as a square inch or inch cable.

Even a big inverter would be unlikely to use a cable bigger than 95mm2 which has a copper diameter of about 11mm.

As to hole size, again some might describe it as an eight zero hole ‘assuming’ you understand the second figure is the decimal.

 

unfortunately, I am now wondering if the guy that gave you the dimensions was being deliberately vague/awkward. 

 

so my guess based on not a lot, is you have a lug on a 25mm2 cable with an 8mm fixing hole.

Edited August 25, 2019 by Chewbacka

[WotEver]

38 minutes ago, Chewbacka said:

so my guess based on not a lot, is you have a lug on a 25mm2 cable with an 8mm fixing hole.

That sounds like a reasonable guess from the available info

[cuthound]

4 hours ago, BlueStringPudding said:

Yeah, I've done the drilling thing once before too But It was thinner metal, this lug will need to be meaty. 

 

The damaged lug/cable and the bolt were measured as best as they could be reached at the time, but the measurement is wrong.  There's no way the negative bolt is 80mm in diameter! ? It's a long and fat cable so could be an expensive mistake If I replace it wrongly. The lug came off while the batteries were being replaced and I think it's being held together with gaffer tape at the moment. So I need to replace it soon as, really. I just can't physically get into the engine bay myself so I'm weighing up what my options are with replacing it.

 

I will have to buy the cable already made up. That's what I did before although it's still broken.

The earth bolt is already there. I'm not changing bolts. Just buying a new cable.

 

What you need is one of these to measure the bolt. It can also measure holes ?

 

https://www.screwfix.com/p/magnusson-digital-vernier-caliper/7093V?tc=WT7&ds_kid=92700043549408090&gclsrc=aw.ds&ds_rl=1241687&ds_rl=1245250&ds_rl=1244066&gclid=CjwKCAjw44jrBRAHEiwAZ9igKMEqDpdMW23msSutyaZvgM4h9CwwMRGC2Ct02HXvG-6Kyw1iDLoUUxoC2pgQAvD_BwE

Edited August 25, 2019 by cuthound
Forgot to add the link. Doh

[Jen-in-Wellies]

17 minutes ago, cuthound said:

 

What you need is one of these to measure the bolt. It can also measure holes ?

 

https://www.screwfix.com/p/magnusson-digital-vernier-caliper/7093V?tc=WT7&ds_kid=92700043549408090&gclsrc=aw.ds&ds_rl=1241687&ds_rl=1245250&ds_rl=1244066&gclid=CjwKCAjw44jrBRAHEiwAZ9igKMEqDpdMW23msSutyaZvgM4h9CwwMRGC2Ct02HXvG-6Kyw1iDLoUUxoC2pgQAvD_BwE

One of these is incredibly useful for boat owners. There are cheaper examples, but very handy to have.

 

Jen

[Tony Brooks]

Personally I would prefer a mechanical version, preferably with just the vernier scales so it never needs batteries and is always ready to take measurements. Not that I ever nowadays need to measure closer than to half a mm

[rusty69]

3 minutes ago, Tony Brooks said:

Personally I would prefer a mechanical version, preferably with just the vernier scales so it never needs batteries and is always ready to take measurements. Not that I ever nowadays need to measure closer than to half a mm

Whenever I get my ancient mitutoyo vernier out, once in a blue moon, the battery is flat. I spend ages finding a new one,by which time I have forgotten what I wanted measure. 

 

Rumour has it, it is your birthday today. If so, many happy returns. 

[Tony Brooks]

3 minutes ago, rusty69 said:

Whenever I get my ancient mitutoyo vernier out, once in a blue moon, the battery is flat. I spend ages finding a new one,by which time I have forgotten what I wanted measure. 

 

Rumour has it, it is your birthday today. If so, many happy returns. 

 

Thanks but no, it was last weekend

[rusty69]

Just now, Tony Brooks said:

 

Thanks but no, it was last weekend

Oh, a week out Happy birthday for last weekend then. 

[Tony Brooks]

Thanks but at 75 I am more than grateful I still seem to have most of my marbles. Probably explains why I like mechanical things.

[rusty69]

6 minutes ago, Tony Brooks said:

Thanks but at 75 I am more than grateful I still seem to have most of my marbles. Probably explains why I like mechanical things.

Well, my old dad at 82 is still gliding and boating.Apparently 120 is the new 40

Edited August 25, 2019 by rusty69
Spelling.

[Paul C]

You don't need to measure the stud. Just measure a nut, or know that its eg M8 or M10. Then try it on the stud, if it screws on okay then you've found the right size. For the pedants, yes there's different threads too but its unlikely anything other than normal thread. (And imperial).

[WotEver]

19 minutes ago, rusty69 said:

Whenever I get my ancient mitutoyo vernier out, once in a blue moon, the battery is flat. I spend ages finding a new one,by which time I have forgotten what I wanted measure. 

I only had this conversation last week when I pulled out my digital calliper to find a flat battery and grabbed a mechanical vernier instead. The chap I was with suggested I follow his example and always remove the battery after use. I might even keep a spare in the box.