INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

SCCR Ratings

SCCR Ratings

(OP)
Where I work we manufacture a machine delivered as a stand-alone enclosure comprising inside a small control panel which holds some relays, the PLC, the HMI, and terminals for controls. The rest of the power components are laid out inside the main stand-alone enclosure (MCCB, VFD, Input reactor, sine filter, transformer, etc.). The customer needs to bring 480V to the machine with the option to bring the cables in through the top, directly to the MCCB, or through the bottom to a set of terminal blocks factory connected to the MCCB. My question is regarding the UL508A requirement for the SCCR. In my mind, coming through the top, we achieve 65kA due to our MCCB. Other components downstream are sized to handle it too, in the way they are protected. No problem.

My concern is when power is fed from the bottom and brought to the terminals first. They are Weidmuller WFF300, and their SCCR is that of untested power distribution blocks, which is 10 kA according to table SB4.1 of UL508A. This is clearly a bottleneck for me, unless we can disregard these, as they are themselves enclosed in a sub compartment of the main stand-alone enclosure. I read again and again on the matter and could not find a satisfactory answer to this specific case. Obviously, in some installations, it will make a huge difference if the customer specs out a SCCR the unit should be capable of handling.

Anybody knowledgeable with UL 508A SCCR?

RE: SCCR Ratings

You would need to get terminal blocks with a higher rating. It would not matter where the terminal blocks are located, any device in the power circuit is part of the SCCR listing, and the lowest level device sets the maximum rating, unless specifically tested and listed as a combination, which you will not find with terminal blocks.

There are many brands and models of power terminal blocks that are listed with a high SCCR, you just can't use that particular one.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close