Busbar Installation

[Folkert.Tazelaar@Kpnmail.]

Are there any standards on installing busbars? My concern is that busbars (opposite to cables) are, due to production- and assembly-tolerances, not always seated flat onto the surface. Closing the gap by torquing the bolt(s) is in my view for several reasons not OK especially when it concerns busbars thicker than 10mm. I would like to see standards developed with guidence for gap measurement and torque values.
Further given the many incidents of busbars coming loose in operation, I would like to see some standardized guidance in selecting selflocking (all Metal) nuts or high quality locking washers.

 

[petersonra]

Are there any standards on installing busbars? My concern is that busbars (opposite to cables) are, due to production- and assembly-tolerances, not always seated flat onto the surface. Closing the gap by torquing the bolt(s) is in my view for several reasons not OK especially when it concerns busbars thicker than 10mm. I would like to see standards developed with guidence for gap measurement and torque values.
Further given the many incidents of busbars coming loose in operation, I would like to see some standardized guidance in selecting selflocking (all Metal) nuts or high quality locking washers.

As far as I know, bus bar assemblies are generally torqued in place.

I don't recall ever having run across a bus bar that has come loose.

I have been known to specify belleville washers, but I think regular split lock washers are adequate.

 

[tom baker]

Is this for NEC products or IEC?
For US look at NEMA and or UL.

 

[Folkert.Tazelaar@Kpnmail.]

As far as I know, bus bar assemblies are generally torqued in place.

I don't recall ever having run across a bus bar that has come loose.

I have been known to specify belleville washers, but I think regular split lock washers are adequate.

When the a (stiff) busbar is torqued in place, the residual pretension needed to lock the nut is affected.
The effectivity of spring washers like belle villes and certainly split lock washers to prevent loss of pretension is limited. In some industries they are even banned for this reason.
I have encountered several cases of loose busbars, in one case even leading to a near aircraft crash.

Is this for NEC products or IEC?
For US look at NEMA and or UL.

It's likely IEC but I will also check NEMA. Thanks Tom

 

[paulengr]

When the a (stiff) busbar is torqued in place, the residual pretension needed to lock the nut is affected.
The effectivity of spring washers like belle villes and certainly split lock washers to prevent loss of pretension is limited. In some industries they are even banned for this reason.
I have encountered several cases of loose busbars, in one case even leading to a near aircraft crash.

It's likely IEC but I will also check NEMA. Thanks Tom

Belleville washers are more intended to help with thermal growth to avoid overstretching fasteners.

Also as it is easy to greatly increase current with the increased surface area but the consequence is greatly increased torque especially during short circuits. So mounting strength is critical.