4 Pole Switch with Neutral Make before phases and break after phases

[akhill1f]

Hi All,

In one of my project, requirement is of providing for 4 Pole Switches for Power distribution in Hazardous area. Requirment also states that in 4 Pole Switch, Neutral shall make before phases and break after phases. Can someone help, whether such products are available or not? if Yes, then forward me the linke / details. Also explain the necessity of such requirement. May be to ensure that no return voltage is available in hazardous area which can lead to the accident, but then this could have been met with any normal 4 pole switch.

Please respond.
Thanks

 

[waross]

This is a common requirement for transfer switches. It is to prevent "open neutral" situations.
I have several times over the years encountered events where equipment was destroyed as a result of a neutral going open.
On one occasion the event was caused by a knife switch opening the neutral before the line contacts were open.
Another issue is protection. Many codes require the neutral to be grounded at one location only. Many ground fault protection schemes depend on a single connection between the neutral and ground. Protection issues arise with generator ground connections and the solution is often solved by switching the neutral.
You are correct that simultaneous operation may be adequate, but if the bid documents call for a late break neutral, then the customer should be willing to pay the extra cost. Some codes accept simultaneous operation but the code is a minimum requirement and if the designer has called up a late break neutral, then you need a late break neutral. If you missed this detail at the biding stage your only consolation is that you are not the first contractor to do so.
Be prepared to spend a lot of money. Late break switches are hard to find and generally quite expensive.
Most Automatic Transfer Switch manufacturers have a late break option available.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Kiribanda]

akhill1f,
Buying a 4-pole open type (delayed) transfer switch with the sweeping neutral is not a problem on low voltage. But the problem will be to find such a transfer switch certified for hazardous area use.
Because the switch enclosure shall be flame (explosion) proof whether you install it in Div 1 or Div 2 (Zone 1 or 2) areas. You cannot use a general purpose enclosure. Are you not looking with that provision for your application?

 

[akhill1f]

Thanks for quick responses. Few clarifications which could be useful for you to give appropriate advise. We are selecting zone II certified EExd enclosure, that and cost both is not a problem. Application is not for auto transfer, these feeders will feed to lighting circuits and welding receptacles located in the field. Earlier we have been using 4 pole MCCB or SFU foe feedig such circuits which are enclosed in EExd enclosure but those were with normal 4 pole MCCBs. Now we want early make and late break neutral pole as stated in original message. Please advise if you are aware about any such product range of SFUs/ MCCBs from reputed OEMs like ABB, Schneider or so. Thanks for your advise. Typical rating would be 16/32/63 Amp and 440 Volts