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Cost Effective Interposing Relays / DC MCBs

Cost Effective Interposing Relays / DC MCBs

Cost Effective Interposing Relays / DC MCBs

(OP)
Greetings

I need the manufacturers names who can provide cost effective Interposing Relays and DC MCBs for Switchgears. Both items shall be UL listed.

Big names offer high prices because of their names. I will appreciate your feedback.

Thanks

RE: Cost Effective Interposing Relays / DC MCBs

ABB have a good range of DC-rated MCBs which are rated for at least 220V service. You will have to check they are UL-qualified though.

What do you need from the interposing relay? Clifford & Snell's D series is first class, and although not 'cheap' per se I would say they are cost-effective. Areva's Prima range was also reasonable, although I'm not sure whether it went to Schneider or Alstom after the breakup of Areva.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Cost Effective Interposing Relays / DC MCBs

(OP)
I need to use Interposing relays for Breaker Open and Close circuit. ABB and other big names are costly. For cost saving we are looking for rather small name with good quality.

RE: Cost Effective Interposing Relays / DC MCBs

Not an application where you should use cheap relays. The major mfrs have type tested certified equipment in their catalogs. Avoid using the common ice-cube relays on 125 or 250V DC circuits. They often cannot break the DC current to an inductive load. The open contact break distance can be too small and the contacts may weld upon closure. Consider the consequences of that...

rasevskii

RE: Cost Effective Interposing Relays / DC MCBs

As raveski says, switching DC is not the same as switching AC. You must start by specifying the DC VOLTAGE you are working with, that eliminates a lot of the available choices.

As to your "smaller less expensive options", it is a poor criterion for an engineering decision. What you will find is that designing testing and manufacturing a proper DC rated relay is expensive. Then the economies of scale are not there to keep the cost low because they are not nearly as universally used as AC relays. So small companies are not going to be able to afford making "cheaper" versions because they will not sell enough of them to justify the considerable investment.

Just pick a good quality relay that fits your needs and negotiate as good a deal as you can up front, then move on. For something as low volume as Switchgear Control applications, you have likely already wasted more money that you can possibly save just by reading this post.

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RE: Cost Effective Interposing Relays / DC MCBs

What rasevskii said.  Use of interposing relays on energize-to-trip circuits should be avoided whenever feasible.  Use of cheap interposing relays on such circuits is false economy and bad design.

I've seen little octal-base plug-in relays used in this application that failed on the first trip.   

RE: Cost Effective Interposing Relays / DC MCBs

The only type of "interposing" relay I'd ever consider on a trip circuit is a good old Electroswitch LOR. Even then I'd be inclined to directly trip the breaker also.  In this type of equipment there is a great deal of "you get what you pay for" and cheap ain't good.  

RE: Cost Effective Interposing Relays / DC MCBs

Further to rasevskii's comments, while it was not on interposing duty, On a trouble call I found a good quality double break relay with two poles in series BUT not rated for DC. It had failed to interrupt the current of an inductive load and had started four arcs in series across the four breaks. The arcs melted the silver contacts and the silver flowed together in a miniature hour glass, on all four breaks. I kept that set of contacts with the miniature silver alloy hourglasses for years.
Contacts welding closed is bad enough but contacts welding closed when trying to open may be worse.
Bottom line: be very careful interrupting DC current.

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

RE: Cost Effective Interposing Relays / DC MCBs

As alternative we use sometimes 2 auxiliary relays 125VDC in parallel:
1- very fast , cannot break the DC current to an inductive load.
2- very slow , can break the DC current to an inductive load.
 

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