3-phase Automatic Transfer Switch (ATS) - Page 1
Forum section: electronics / beginners

author: negative_feedback
author_rank: Contributor
timestamp: October 06, 2023, 03:13:03 pm
content: I have to connect 3-phase 230VAC resistive load over ATS (Automatic Transfer Switch) of some sort. Source A and B would be both 230VAC mains, but on different power meters (longest absolute cable run <40m).Heater (12kW) sometimes uses 1 phase and sometimes all 3 and it is wired as 3P + 1N + 1PE.There was a similar discussionherebut it was about single-phase load.Options so far:1) Cheap changeover switch from AliExpress (TOMZN 4P/125A) - if we control primary source with MCB then it would be in semi-automatic mode. This is the only way I would use these uncertificated devices (additionally, On-Delay relay);2) Two 25A 4P contactors, mechanically or electrically interlocked;3) AIO device from SE/ABB/Hager will be installed after initial test run.It would be swell if someone can explain this to me:Q1: Why I have to use 4P switching equipment instead of 3P (can I use two 3P contactors for ex.)?Q2: What should be used for safety/controlling of ATS, 3P MCB or 4P (RCCB, its hard to find 4P MCB) ?Q3: Should I worry about phase sync, one meter is digital and the other is analogue.

author: themadhippy
author_rank: Super Contributor
timestamp: October 06, 2023, 03:30:48 pm
content: Quoteuk regs at least require all live conductors to be broken for safe isolation,it also classes the neutral as live conductor.Quotechange suppliers, my local wholesaler has 4 pole devices on the shelf,or will order in anything too exoticQuotenot unless your trying to parallel the 2 supplies up,however best to check the phase rotation just in case someone decides to chuck in a 3 phase motor

author: rogerggbr
author_rank: Contributor
timestamp: October 06, 2023, 04:11:07 pm
content: Advantage of dedicated changeover unit (i.e. 8 pole) is the interlocking is built in and power stays on even if your controls are dead, manual changeover still possible. Ditto MCCBs. Contactors have the advantage that they fail safe and both drop out on control fail. You decide which way to go.As pointed out above, it is normal to break the neutral as you may not have control of the upstream supplies and joining neutrals could be bad so 4P switching is safer.For controls the easiest is bias A on, B on if A fails, can just do this with a couple of timers. In industry you would use a phase fail relay to detect loss in any phase as well as voltage drop. It is usual to add timers to the process to ensure no race conditions, there are many dedicated units available of course.The phases would normally be synced, but this is assuming loads with motors. If your load is guaranteed resistive only then of course no need to bother, but it would still be good practice.

author: negative_feedback
author_rank: Contributor
timestamp: October 06, 2023, 04:52:39 pm
content: I understand it is more safe to use 4P but discrepancy in availability between 3P and 4P is ridiculous. That's why I thought 3P can do the job. What would be the worst case scenario with resistive loads?I was checking TME.eu but I couldn't find dedicated units from SE/ABB, what supplier you use now in the UK?

author: themadhippy
author_rank: Super Contributor
timestamp: October 06, 2023, 05:03:59 pm
content: Quoteif you mean for 4 pole mcbs either a local independent wholesaler or city electrical factors,https://www.cef.co.uk/catalogue/categories/mcb-s-miniature-circuit-breakers-four-pole-mcb-sboth are electrical wholesalers not an electronics supplier

author: Jeroen3
author_rank: Super Contributor
timestamp: October 06, 2023, 05:25:02 pm
content: Quote from: negative_feedback on October 06, 2023, 03:13:03 pmCode says (nen1010):You may omit switching neutral if the network operator guarantees the neutral to be reliable low impedance to earth, only in TN-C-S and TN-S systems.In residential or living spaces neutral must always be switched.So.. 4p contactors. 3p may also mess up upstream differential protections.Quote from: negative_feedback on October 06, 2023, 03:13:03 pmSee above, 4p. Andno.Quote from: negative_feedback on October 06, 2023, 03:13:03 pmYou should at least keep the sequence the same. Since you only have loads, and no producers this isn't that much of a concert if your loads can take it.Is this in belgium with a 230V delta system??

author: negative_feedback
author_rank: Contributor
timestamp: October 06, 2023, 05:42:57 pm
content: Quote from: themadhippy on October 06, 2023, 05:03:59 pmI was interested in availability of SE TransferPacT or ABB Compact ATS. For 4P versions I have to place an order and wait.Quote from: Jeroen3 on October 06, 2023, 05:25:02 pmNo, NL. How does Hager compare to SE/ABB?