Built 120/208 bank. Spec had a ferro switch. Floating neutral bus.

[bobbo]

Understand floating neutral bus.

We had a double run of 350 secondary, with 50 cans, wye primary, 120/208. Spec had a ferro switch for the floating neutral bus to ground.

when I think of ferro resonance, think of primary cable length to KVA of a pad mount.

With only 80 feet of secondary cable and 3 50 KVAs, could you ferro the secondary cable?

So you have the ferro switch closed when you closed before you close your primary switches.

But it's wye secondary, so the only circulating current is from the neutral from can to can.

I don't know now how you can hi-pot the secondary with a wye wye hook up. A straight delta secondary hook up we grounded one phase to get rid of circulating current on the secondary between the cans.

does anyone have ferro switches and what set up would you use them?

[rob8210]

Am I missing something? You said wye primary , 120/208 wye secondary , right? But you also said floating neutral buss? Just asking to be clear, so the secondary buss neutral is floating and there is no ties to the primary neutral which is grounded, correct? It seems weird that the secondary neutral is not grounded, it must be hooked up to a grounded service, right? Or is this one of those situations where a wye/ wye bank is built , neutral is supplied to the customer but not necessarily used? It does not make sense to me to have a floating secondary neutral . Also we tie all neutrals together , primary and secondary

[Electriceel]

Y primary,Y secondary voltage, you will need to bond the primary neutral bushings together in a continuous loop to the primary neutral conductor.
Secondary neutrals will all need to be bonded together and tied to the primar neutral.
If you don't bond the primary your secondary phase to phase voltage will be high and low depending on customer load.

[Nate]

Not sure why you would need to float the neutral on this type of bank. The only time you should float the neut is on a Closed wye/delta bank. You should jumper the between the floating and primary neutral before you open the LBU,s or cutouts. So that you don't get a flashover.

[bobbo]

Everything else was a conventional hook up. Secondary was hooked up to pole ground, primary nuetral.

but there was a floating primary nuetral bus.

but there was a switch that tied a everything, pole ground, nuetral and the Secondary nuetral. To that floating primary bus. You closed that when you closed the can in. And when you have all your phases closed in. You opened it.

they called it a ferro switch. To me ferro has to deal with Primary cable length and pad mounts, not a 120/208 bank with secondary URD about 80 feet and two runs.

never seen a set up like it. But it was in the spec.

if you had single bushing cans to make up that bank, you wouldn't have that switch.

277/480, I have seen that spark gap thing for inrush current that you put on a leg and ground. But that was delta primary.

wye primary, never seen it?

[bobbo]

Am I missing something? You said wye primary , 120/208 wye secondary , right? But you also said floating neutral buss? Just asking to be clear, so the secondary buss neutral is floating and there is no ties to the primary neutral which is grounded, correct? It seems weird that the secondary neutral is not grounded, it must be hooked up to a grounded service, right? Or is this one of those situations where a wye/ wye bank is built , neutral is supplied to the customer but not necessarily used? It does not make sense to me to have a floating secondary neutral . Also we tie all neutrals together , primary and secondary

Only the topside primary bushing neutrals were floating.

i just built the picture.

[bobbo]

Am I missing something? You said wye primary , 120/208 wye secondary , right? But you also said floating neutral buss? Just asking to be clear, so the secondary buss neutral is floating and there is no ties to the primary neutral which is grounded, correct? It seems weird that the secondary neutral is not grounded, it must be hooked up to a grounded service, right? Or is this one of those situations where a wye/ wye bank is built , neutral is supplied to the customer but not necessarily used? It does not make sense to me to have a floating secondary neutral . Also we tie all neutrals together , primary and secondary

Topside primary bushings for nuetral were floating. And this "ferro" switch as they called. Kept the topside nuetral tied to all nuetral and then you opened the switch to make it floating. What's the advantage of it?

[lewy]

Topside primary bushings for nuetral were floating. And this "ferro" switch as they called. Kept the topside nuetral tied to all nuetral and then you opened the switch to make it floating. What's the advantage of it?

I must be missing it as well we only float the neutral on a wye primary delta secondary, everything else all the neutrals are tied together.

[rob8210]

Hey Bobbo. I understand what your saying , just have never seen such a thing. But like you if it is the specs that is what i will build. I can't see the reasoning for it ferro resonance isn't really an issue except in situations with higher primary voltage, and not really a concern around here except in some underground situations involving longer runs of primary cable( capacitance) .

[bobbo]

Hey Bobbo. I understand what your saying , just have never seen such a thing. But like you if it is the specs that is what i will build. I can't see the reasoning for it ferro resonance isn't really an issue except in situations with higher primary voltage, and not really a concern around here except in some underground situations involving longer runs of primary cable( capacitance) .

To me, the way I was trained and taught had everything to do with length of cable and a three phase pad mount KVA. In a ferro situation, the only way to close is take off the secondary load or gang switch the primary.

some retired man was calling this basically grounding switch for the primary floating bus a ferro switch, which is inaccurate.

A lot of places want the topside nuetral bus for wye primary. And I don't understand why? Especially with wye secondary. A straight delta Secondar I understand because of circulating current when you close one at a time, and you have a lot of current.

Can someone tell me why you need a floating nuetral bus on the topside nuetral primary bushings?