Distribution Board Rating

[Jeffmo65]

Hi , quick question , in my thoughts requires a quick answer
160amp fused switch feeding existing Hagar panel board fine no problem with that
My superior wants to install a new 125amp rated DB fed from same switch ?
I don't I would want to see a board rated at 160amp or above
Thoughts please

 

[Engineer54]

Hi , quick question , in my thoughts requires a quick answer
160amp fused switch feeding existing Hagar panel board fine no problem with that
My superior wants to install a new 125amp rated DB fed from same switch ?
I don't I would want to see a board rated at 160amp or above
Thoughts please

Why?? Just change the fuses out to 125A.
The size of the fuse switch is basically just a frame size, same as a DNO's service cut out, where the max fuse rating is say a 100A, but can accomodate anything from say 20A to 100A

 

[telectrix]

think OP means a 2nd 160A DB parallelled with an existing 160A DB, both on a 160A fuse

 

[Jeffmo65]

Correct . Can't change the fuse . The rating as far as I gather is the bus bars in the board . Surely they must be rated to the protective device ?

 

[Engineer54]

think OP means a 2nd 160A DB parallelled with an existing 160A DB, both on a 160A fuse

If that's the case, still can't see any real problem, if the 160A switch fuse supply is sufficient to cover the needs of both DB's.

 

[Darkwood]

The 160amp fuse is there to protect the submain cable, any switchgear attached should be rated to the upstream fusing i.e. 160A in this case unless due to design parameters where the board cannot pull more than the main switch can handle due to say the sum of the protective devices downstream limits possible FLC (Although its good practice to match the switchgear even in this case to allow for expansion and alteration).

2 x 160amp off one is fine if demand has been worked out to satisfy this set up, although I would have the 160amp front end feed a small busbar chamber and 2 individual Isolators for the DB's

 

[Engineer54]

Correct . Can't change the fuse . The rating as far as I gather is the bus bars in the board . Surely they must be rated to the protective device ?

Why can't you change the fuse(s)??

Would you design an installation where the total current expected of the individual circuits of a DB is going to be in excess of the rating of the DB, i HOPE NOT!!

 

[Jeffmo65]

Why can't you change the fuse(s)??

Would you design an installation where the total current expected of the individual circuits of a DB is going to be in excess of the rating of the DB, i HOPE NOT!!

Eng I havnt designed anything this is an existing supermarket with existing distribution connected and yes your right about the design aspect . However someone far more worthy than me has done this previous . This scenario is an add on which I am arguing with my gaffer about . In essence I see the bussbar as just a link of copper so therefore the fused switch device is there to protect the sub feed and the links through the DB . I appreciate that some maths wizard will whistle of some equation about withstand and PSCC and all that which would be fine . But trust me my boss would look at it and throw it in the bin cos he wouldn't understand it . The design with regards to bussbar chamber I had thought of . Costs prevail unfortunately . Thanks guys

 

[Engineer54]

The 160amp fuse is there to protect the submain cable, any switchgear attached should be rated to the upstream fusing i.e. 160A in this case unless due to design parameters where the board cannot pull more than the main switch can handle due to say the sum of the protective devices downstream limits possible FLC (Although its good practice to match the switchgear even in this case to allow for expansion and alteration).

2 x 160amp off one is fine if demand has been worked out to satisfy this set up, although I would have the 160amp front end feed a small busbar chamber and 2 individual Isolators for the DB's

Providing the 160A switch fuse supply is sufficient to supply both of these DB's then like you the inclusion of a busbar chamber and isolators/switch fuses for the DB's is the way i'd go too. However i can't see why you'd need both DB's to be rated to the 160A switch fuse....

 

[Jeffmo65]

Thanks Eng . Like you the buss chamber with the two isolators is the way forward . Another option maybe would be to have another sub feed from the existing switch feeding an 125amp switch fuse then into an 125amp rated DB ? . I understand the outgoing would in theory limit the draw but knowing how they work someone else will probably come along and drop another say 63amp breaker in there for some humongous bit of kit and I would worry the board would not be sufficiently rated and guess what it's my arse that's on the dotted line . Cheers