HR Joint

[cuthound]

An ex-colleague sent me this graphic example of a high resistance joint.

 

I thought I would share it so that people can understand why clean and tight joints are necessary.

 

 

 

 

Edited April 25, 2022 by cuthound
Phat phingers

[MtB]

Excellent!

 

I'm not surprised the joint is high resistance made with that red plastic nut... 😂

[Guest]

18 minutes ago, cuthound said:

An ex-colleague sent me this graphic example of a high resistance joint.

 

I thought I would share it so that people who don't understand why clean and tight joints are necessary.

 

 

 

 

 

When we had a kitchen fit done in 2017 we had a similar connection found in our consumer unit.

Edited April 25, 2022 by The Happy Nomad

[ditchcrawler]

23 minutes ago, cuthound said:

An ex-colleague sent me this graphic example of a high resistance joint.

 

I thought I would share it so that people who don't understand why clean and tight joints are necessary.

 

 

 

 

I burnt my finger on a chockblock that was used to extend the cables on a 12 volt water pump, it was dropping 4 volts across it

[PeterScott]

 

Gosh, and I thought the Personnel Director must have a dodgy knee.

Edited April 26, 2022 by PeterScott
knee pic

[Jen-in-Wellies]

18 hours ago, MtB said:

Excellent!

 

I'm not surprised the joint is high resistance made with that red plastic nut... 😂

Where can I buy some of those brightt red nuts? Ideal to distinguish the positive from the negative bus bar.

[Peugeot 106]

In days of yore when I was a teenager i had a Morris minor with positive earth. I bought a cheap 8 track (remember them?) with negative earth. I had 2 x10” speakers in a massive plywood box full of insulation taking up the whole back seat! I isolated the case in an old welly boot and reversed the connections and connected direct to the battery. No fuse. One day smoke was billowing from it so I reached under the dash while still driving, wrenched  all the wires out and burned my hand.

you live and learn sometimes the hard way. It was very painful 

[blackrose]

18 hours ago, ditchcrawler said:

I burnt my finger on a chockblock that was used to extend the cables on a 12 volt water pump, it was dropping 4 volts across it

 

Why would a chockblock do that exactly? Was it the quality of the metal in the chockblock that was dodgy or the cable connections? Just wondering as I sometimes use them too.

19 hours ago, cuthound said:

An ex-colleague sent me this graphic example of a high resistance joint.

 

I thought I would share it so that people can understand why clean and tight joints are necessary.

 

 

 

 

 

The thing that strikes me is that those connections don't appear particularly dirty or loose, so what's happened?

 

Also I'm not quite sure what I'm looking at in the picture? Is there a strip of metal behind the long terminal board like a big busbar?

Edited April 26, 2022 by blackrose

[cuthound]

43 minutes ago, Peugeot 106 said:

In days of yore when I was a teenager i had a Morris minor with positive earth. I bought a cheap 8 track (remember them?) with negative earth. I had 2 x10” speakers in a massive plywood box full of insulation taking up the whole back seat! I isolated the case in an old welly boot and reversed the connections and connected direct to the battery. No fuse. One day smoke was billowing from it so I reached under the dash while still driving, wrenched  all the wires out and burned my hand.

you live and learn sometimes the hard way. It was very painful 

 

I had similar, but reversed the polarity of the battery by turning it around and the flashed the field coils of the generator to reverse the polarity of that.

 

It worked perfectly for the time I had the car.

Edited April 26, 2022 by cuthound
To change "could" back to wot I rote, "coil".

[cuthound]

44 minutes ago, blackrose said:

 

The thing that strikes me is that those connections don't appear particularly dirty or loose, so what's happened?

 

Also I'm not quite sure what I'm looking at in the picture? Is there a strip of metal behind the long terminal board like a big busbar?

 

The bus bar looks dirty to me, and some attempt had been made to clean it, but not the half with the HR joint on it.

 

I suspect a combination of a dirty bus bar and a connection that either wasn't properly torqued down or which has come loose has caused the HR 

 

You are looking at a bus bar in a switchboard. I think the "strip of metal" behind the busbar is actually a large cable.

[AndrewIC]

The built-in power indicator is quite handy.

[davem399]

The nut holding the dark blue cable is only on by about one thread as well.

[cuthound]

21 minutes ago, davem399 said:

The nut holding the dark blue cable is only on by about one thread as well.

 

Yes, it would be OK if that cable didn't have a nut underneath it. Luckily it is a small, low power cable.

[Peugeot 106]

2 hours ago, cuthound said:

 

I had similar, but reversed the polarity of the battery by turning it around and the flashed the field coils of the generator to reverse the polarity of that.

 

It worked perfectly for the time I had the car.

I wasn’t clever enough in those days and confess i’m probably not much cleverer now. But I do know now that if it can go wrong it probably will the only difference being that I used to  bash on with things in glorious ignorance. These days I tend to worry and overthink problems which can also be a hindrance. There seems to be no happy medium!

[GUMPY]

I would suspect that the bar wasn't that dirty down the far end, my first thought is that it is discolouration due to excessive heat.

[ditchcrawler]

2 hours ago, cuthound said:

 

I had similar, but reversed the polarity of the battery by turning it around and the flashed the field coils of the generator to reverse the polarity of that.

 

It worked perfectly for the time I had the car.

Done that to many a car

[cuthound]

17 minutes ago, Loddon said:

I would suspect that the bar wasn't that dirty down the far end, my first thought is that it is discolouration due to excessive heat.

 

If you look closely at the bus bar, the clean end has lots of light scratches and the odd black bit on it, which gave me the impression someone had cleaned that end.

 

I agree the heat may well have caused discoloration though.

[GUMPY]

The main question for me is what was trying to draw that amount of current to generate that heat. Its certainly nothing small.

[cuthound]

7 minutes ago, Loddon said:

The main question for me is what was trying to draw that amount of current to generate that heat. Its certainly nothing small.

 

The bus bar is part of a mains switchboard feeding operational equipment in a telephone exchange, so likely to be feeding the DC power plant or air conditioning units.

 

Whilst most of the exchanges use 100 amp DC modular swithed mode rectifiers, some of tne older ones still have 2000 amp DC rectifiers. However there is nothing in the photo to give a sense of scale, so difficult to guess the cable sizes.

[twbm]

This was a cross threaded and thus not tight 12v connection on my brand new car last year.  The bit thats missing is a melted, but not blown, 200amp fuse and the other post.  About two minutes away from the plastic catching fire when we found the problem.  

 

[mrsmelly]

1 hour ago, ditchcrawler said:

Done that to many a car

Me too.

[bizzard]

4 hours ago, cuthound said:

 

I had similar, but reversed the polarity of the battery by turning it around and the flashed the field coils of the generator to reverse the polarity of that.

 

It worked perfectly for the time I had the car.

You would have needed to swap the two low tension wires around on the ignition coil too.

Edited April 26, 2022 by bizzard

[Mike Todd]

3 hours ago, Peugeot 106 said:

I wasn’t clever enough in those days and confess i’m probably not much cleverer now. But I do know now that if it can go wrong it probably will the only difference being that I used to  bash on with things in glorious ignorance. These days I tend to worry and overthink problems which can also be a hindrance. There seems to be no happy medium!

I look back in horror at the things my parents got me to do in maintenance on their car in 1960s! Included changing brake pads by inspection and from first principles!

[Chris Lowe]

On 25/04/2022 at 17:22, cuthound said:

An ex-colleague sent me this graphic example of a high resistance joint.

 

I thought I would share it so that people can understand why clean and tight joints are necessary.

 

 

 

 

 

I had the fire briagde out once becuase the main input fuse was hot and melting in the bungalo i was renting, they gave their newbie the bolt cutters and chopped the cable,there was pitch dripping everywhere.

But at least they cut the cable where the power company could still fix it easy.

 

 

 

This was cuased by the connection working loose.

Edited April 26, 2022 by buccaneer66

[MtB]

6 hours ago, bizzard said:

You would have needed to swap the two low tension wires around on the ignition coil too.

 

Yes! 

 

But I was too thick to understand why....