i am designing a 3 phase transfer switch for genset backup using 2 interlocked magnetic contactors, the question is do i need to switch the neutral or can i keep a sold neutral as i can find 3 pole contactors ok but the 4 pole type are not so easy to find.

 

perhaps this is a good question for crossy to help with

 

thanks

It is normal not to switch the neutral in a 3-phase transfer.

 

Even if you find a suitable 4-pole contactor it is vital that you use one with a "late" neutral contact that opens last and closes first to avoid having an open neutral on an energized and unbalanced 3-phase system.

 

Don't forget to incorporate both electrical and mechanical interlocks to make absolutely certain that both contactors cannot be energised at the same time.

 

For USD 40 is it worth designing your own? https://www.aliexpress.com/item/4P-63A-MCB-Q6-63-4P-type-Dual-Power-Automatic-transfer-switch/2028405861.html?spm=2114.30010308.3.41.9nR925&ws_ab_test=searchweb0_0,searchweb201602_4_10065_10068_10084_10083_10080_10082_10081_10060_10061_10062_10056_10055_10054_10059_10099_10078_10079_10073_10097_10100_10096_10070_10052_10050_10051_424,searchweb201603_2&btsid=6b3d2db0-273d-4f37-8f03-8250f72a1d9a

 

Or for a bit more https://www.aliexpress.com/item/4P-100A-MCB-Q2-100-4P-type-Dual-Power-Automatic-transfer-switch/2028401256.html?spm=2114.30010308.3.113.xNfiTl&ws_ab_test=searchweb0_0,searchweb201602_4_10065_10068_10084_10083_10080_10082_10081_10060_10061_10062_10056_10055_10054_10059_10099_10078_10079_10073_10097_10100_10096_10070_10052_10050_10051_424,searchweb201603_2&btsid=1ea8b2b7-3f8d-49bf-876a-fa7e707c17e4

 

Many more similar items on AliExpress.

 

This is the one I use.

Bought from China.

Seems to do the job for me, infact had the genset running yesterday for a couple of hours due to power outage.




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thanks for the input

 

i want make my own as in the future i will be making to fully automatic with auto start for genset.

 

managed to pick up a couple of mitsubishi 50a 3 pole contactors for 1500 each so not to pricey 

Sounds good

Mine has auto start function, but I only use on manual as when the wind is blowing hard like now, we have lots of flicks.



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