spd on sub panel 120v

[mahendra]

i have recently bought some spds for a long awaited upgrade of my system .I have spds almost any where its needed however i have one problem with the installation of one on a sub panel,See the sub panel was wired directly from the main utility breaker (already have an spd on that) so its with out any separate breaker.The sub panel is pretty far away from the main panel an i want to install an spd on it to protect my sensitive stuff .the manual says one wire(red/black) to AC hot in And one Wire(red/Black) to AC hot out and green to earth ground.See the Problem is i only have the AC hot in .The Ac hot out Are on Four Breakers in want protection for.Is there any way to Wire this so as to protect the entire sub panel with out having to change it for one with a main breaker disconnect (since this Do not have one

[mahendra]

i guess my explanation is not clear ,So here goes.Can any one advise on how i can install a mnspd 300 on a 120v load center/sub panel.The panel does not have a main breaker .Main utility breaker shuts it off and i already have a spd on that but the panel is very far off so i want to put an spd dedicated to that panel.thank you

[boB]

Each SPD has two sections...

If your panel is 120V/240V, I would connect the green (ground) wire of the SPD to
ground (of course) and one main SPD connection to one main bus 120V line and
the other to the other main 120V phase line.   When I say "main", I mean, the
bus the feeds all of the breakers on that circuit.

If you only have one 120V phase or you are on a 230V 50Hz system, connect
one hot line to one SPD half, the other SPD hot line to the other 230V hot line
and of course, the ground (green) SPD wire to ground.

boB

[mahendra]

i have one 120v phase Bob so does that mean that i will be using only half of the spd only?thanks

[mahendra]

Or are you referring to the main lugs in the panel

[boB]

Or are you referring to the main lugs in the panel

Main lugs =equals=  main bus ?  IF so, then yes.

If only one (1) 120V bus,  then you could connect both hot SPD wires to that one 120V leg
for double protection.

boB

[mahendra]

thanks bob

[mahendra]

before i close though Bob can i ask why the neutral line is not wired in AC circuits using the spd.

[Watt]

before i close though Bob can i ask why the neutral line is not wired in AC circuits using the spd.

Is your neutral wire bonded to ground?

[boB]

Well, actually I suppose the neutral could also be one of the wires going to the SPD along with the hot L1 or L2
especially if the ground point is a long ways away from the SPD.  This is because the lightning is a common mode
event and raises both hot and neutral above ground together.

So, the neutral might be connected.  In your case, if you only have the 120V line, then I
would connect the neutral AND hot to the SPD as well as the third ground line.

I think most people would not connect the neutral because they would rather not buy two (2)
SPDs and rather use the 2 halves for the L1 and L2 hot  lines since the neutral is connected
to ground at some point.

Then again, in a PV application where the negative is also grounded (not always !), they will
connect both negative and positive to the SPD.  That's because the lines are
closer to the lightning than they may be to the grounded point and you want to
keep those raised voltage lines  from going too high above ground.

boB

[mahendra]

thanks Bob