**Show Us Your Installs!!!**

[Spudnik]

Right chaps,

Due to a few unavoidable issues, we have lost the original thread and pics etc.

Sorry about that!!!

So, if you want to re-upload your pics then great, if not, give us something new!


Cheers!!

 

[Engineer54]

whats trefoil then?

- - - Updated - - -

Correct!!! lol!!

 

[Silly Sausage]

Saw this today...
Should cleats be reclassified? | Professional Electrician & Installer

 

[t01474]

Good points made by everybody concerned. I'll bear them in mind for future works. Never even considered the tie wrap scenario
Would the same happen with 4-c SWA? Generally you see them just tie-wrapped to the ladder racking, tray, ect.

 

[Stroppy]

I had no idea cables jumped with fault current. Does the impulse come from the large magnetic field generated, or something else?

 

[Stroppy]

Wouldn't expect anything less from someone who has a cyanide and happiness avatar

Thanks, everyone agrees I'm an odd little man! Original cartoon: Cyanide & Happiness #2987 - Explosm.net

 

[pennywise]

I had no idea cables jumped with fault current. Does the impulse come from the large magnetic field generated, or something else?

This illustrates it quite nicely and why the correct type of cleats are needed.

Short Circuit Testing new - YouTube

 

[Stroppy]

Great video, most informative.

For non-mobile users: Short Circuit Testing new - YouTube

 

[Knobhead]

Good points made by everybody concerned. I'll bear them in mind for future works. Never even considered the tie wrap scenario
Would the same happen with 4-c SWA? Generally you see them just tie-wrapped to the ladder racking, tray, ect.

Under extreme fault conditions a SWA can be blown apart. But that would really be worse case scenario.
When singles are used then magnetic repulsion is a real danger. I’ve actually watched bus-bars bending under the start up load of a squirrel cage motor. That came about because a MCC panel had been extended several times without due consideration to the overall effect on the bars. “It’s only a 100HP motor, it’ll be OK.” The trouble was several “it’s only” situations that had happened over the years. To the point where the bars gave up the ghost, bent and shorted out.

 

[High Tower]

Tony and E54 thanks for that I must say I'm taking away some knowledge from this!

 

[Engineer54]

Under extreme fault conditions a SWA can be blown apart. But that would really be worse case scenario.
When singles are used then magnetic repulsion is a real danger. I’ve actually watched bus-bars bending under the start up load of a squirrel cage motor. That came about because a MCC panel had been extended several times without due consideration to the overall effect on the bars. “It’s only a 100HP motor, it’ll be OK.” The trouble was several “it’s only” situations that had happened over the years. To the point where the bars gave up the ghost, bent and shorted out.

I've only ever seen the results of a catastrophic fault on a dual supplied 3200A LV switchboard!! Where the bracing supplied by the manufacturer, was found to be, not up to the fault KA rating of the board. Which should have been 50KA but was in fact, barely reaching 32KA bracing levels. Two complete panel sections needed to be totally replaced and bracing upgraded throughout the entire switch board!! A very expensive exercise for the manufacture, which was only mitigated to a small degree by a wrong doing of the contractor who also ended up paying a pretty price!! lol!!

NOT one of my projects i should hasten to add!! lol!!

 

[Silly Sausage]

Looks like we're dealing with large forces here...

A three-phase short circuit in trefoil formation, the maximum force on the
conductor as detailed in IEC 61914:2009 (Appendix B Equation B.6), is
described by the following:

F[SUB]t[/SUB] = (0.17 x i[SUB]p[/SUB][SUP]2[/SUP])/S

Where
F[SUB]t[/SUB] = Maximum Force per unit length of cable (N/m)
i[SUB]p[/SUB]= Peak short circuit current (kA)
S = Centre-to-centre distance between neighboring conductors (m)

when the currents are in 100s of kA!!!



Interesting stuff!

 

[Knobhead]

Excel went in to E numbers :fuk2:

 

[Engineer54]

Looks like we're dealing with large forces here...

A three-phase short circuit in trefoil formation, the maximum force on the
conductor as detailed in IEC 61914:2009 (Appendix B Equation B.6), is
described by the following:

F[SUB]t[/SUB] = (0.17 x i[SUB]p[/SUB][SUP]2[/SUP])/S

Where
F[SUB]t[/SUB] = Maximum Force per unit length of cable (N/m)
i[SUB]p[/SUB]= Peak short circuit current (kA)
S = Centre-to-centre distance between neighboring conductors (m)

when the currents are in 100s of kA!!!



Interesting stuff!

Fault currents are limited by what the transformer in question can deliver into a fault!! Obviously the larger the Transformers KVA/MVA rating, the more current it can deliver into a fault!! For a typical 240/415V 1000KVA transformer, is roughly about 20KA...

 

[Silly Sausage]

Deleted, note to self, 'Don't attempt any maths after a few beers!'

 

[Knobhead]

So Ip is only 400,000,000 (20K²). That’s OK then :ack2:

It gets worse the more you look at it.

So if we allow 50mm conductor centers:

Ft = (0.17*(20K²))/20 = 3,400,000 N/m

A nylon strap’s going to hold that, isn’t it?