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Relay Test Terminal Blocks

Relay Test Terminal Blocks

Relay Test Terminal Blocks

It is standard practice to install test terminal blocks (TTB) in C&R panels.
The CTs etc. wiring is routed to the relays through test terminal block to facilitate relay testing without disconnecting the CT wires at the relay.
Alstom TTB type MMLG01 is most widely used to my knowledge.
These days, there are TTBs with built-in auto CT shorting facility etc. Alstom P991 is one example.
I would like to know how popular is P991 and similar TTBs of other makes such as Siemens (/Reyrolle), RMS etc.!!

Rompicherla Raghunath

RE: Relay Test Terminal Blocks

Unwiring a relay to test it is just bad, in that it is possible to land the wires on the wrong terminal.

We use the ABB FT switches. They are like the switches on the old ABB relays.
They are much better than the GE PK blocks.
The relay guys here don't like the Euro style test blocks very much. It might have to do with the compact design they don't like. Or something else.

At my old company we had a good Alstom sales engineer, but since he passed away I haven't seen a sales anything in my area.
I did try the MMLG01 test switch with some GEC bus differential relays, and they worked well at the time.

But it's hard to support a product where the manufacturer does not call on us.

RE: Relay Test Terminal Blocks

We also use the ABB Flexi-Test line up of blocking switches. I like them.

RE: Relay Test Terminal Blocks

Two categories, there's the FT switch and then there's everything else... winky smile

We make extensive use of the FT switches for all currents, voltages, and the relay power supply as well as any DC I/O that might need to be intercepted during testing. The Techs have not expressed any desire to change that I'm aware of and even if we did change it would be decades before all of the existing ones could be replaced with something else.

RE: Relay Test Terminal Blocks

Also be careful when you first get discouraged by the price of the ABB FT switch. Just go with it. Don't spend a couple of years using a cheaper knock-off version only to find out some of the handles just fall open sometimes for no reason at all.

RE: Relay Test Terminal Blocks

The MMLG01 and '02 are the industry standard in the UK - been around since long before I was working in the industry.

The newer P991 probably seems like a great idea to someone, but there's been definite resistance to its adoption by the users I am acquainted with. It really doesn't do anything that the MMLG blocks don't already do, and the MMLG's have been around forever - the desire to change must be driven by something other than user demand: manufacturing cost perhaps, or some irrational need for foreign owners to purge the last of the GEC Relays product line...? ponder

RE: Relay Test Terminal Blocks

The ABB/Westinghouse types are favored in my area. The GE PK are NOT, although I see them crop up once in a while, along with FT and wonder why.

I've used the Alstom ones, that were favored here about 25 years ago. The problem, as I see it, is a company should standardize on one type and stay that way. When one ends up in a station without the correct test paddle, it kind of defeats the purpose. I was able to use a zip tie on an Alstom unit until I could get the correct paddle. The proper test paddles are not something that can be ordered quickly or inexpensively.

FWIW, the West/ABB Type FT can be used without the paddle (alligator clips and something to open the "hair pin"). The down side of this is inadvertent operations due to alligator clips falling down on live blades.

The worst I've seen has been large simple cycle gas turbine plants, where there is not a single test switch available. Imagine 8x units with Pri & Sec Xfmr, Gen, BF, OOS relays and no easy way to perform even basic meter and I/O checks in the future.

There is a German company,secucontrol, that makes a very nice unit, similar to an FT with some possible improvements. Other than at trade shows, I've never seen them installed.

RE: Relay Test Terminal Blocks

Test switches are one of those things where one will be pushed away from the present standard rather than pulled to something new. There could be something “better” but still not worth the hassle of changing.

RE: Relay Test Terminal Blocks

Most common I see is the ABB FT switches, but a number of other companies, like ITI, Tesco, Durham and States all show up. I keep a few of the more common ABB switches I see on hand for retrofit work.

I did a project a few months ago at a government facility using the new "Safety Test Switch", https://safetytestswitch.com/ mentioned above
Choice of switch was driven by safety concerns about exposed live parts, after an event at site where a test clip got dropped across a circuit, causing a trip. They worked out well, price was higher per point than an FT switch, the onsite test technicians all seemed to be happy with them, especially the guy who caused the trip.

I have also used on a number of jobs terminal block style test and disconnect switches from companies like Wago, Phoenix Contact and others, mostly I use the Wago products only because the local supplier has very good service and usually has what I need on hand, https://www.wago.com/infomaterial/pdf/51235484.pdf

Really seems there are lots of options, just depends on the level of safety, access and serviceability you need, and if you can get parts and pieces if needed in a timely manner.


RE: Relay Test Terminal Blocks

ABB FT or States are pretty standard around here, leaning a bit towards FT.

They're a known quantity, avoiding the unfamiliarity brought on by newer, more dense designs.

old field guy

RE: Relay Test Terminal Blocks

What, a comment about being stuck in a substation without a paddle.

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