Isolation Transformer (bonded>floating) Back up power

[Leyden Jar]

Condition: In order to power a transfer switch (6 circuit 120V) through a 60 amp sub panel. A floating neutral current must be enabled. In place of a generator is instead a connection to an alternative 120v 15 amp power source dedicated bonded neutral. (Outdoor GFCI 15 amp outlet via extension cord)

Solution: Convert bonded neutral to floating neutral using an isolation transformer. (example: Isolation Transformer)

Problem: When utility power is restored then the house current is effectively bonded neutral.

Equipment: Transfer switch is a UTS6 with many features and has capacity to cut off when power is restored. Only, as an assurance and a certain safe guard there are three cut off switches. 1) Simply, toggle off the 60 amp breaker to sub panel in Main. 2) Switch the Main panel to off. 3) Disconnect from the utility by switching off emergency cut off switch below the meter and above the 100 amp outside service entrance to the Main panel.

Apparatus: Isolation transformers with (Faraday Cage) Faraday Shields are used to produce a magnetic field that charges the coils from the input side coil to the output side/secondary coil. In this condition the floating neutral condition is derived.

Questions: What happens to this condition when the neutral and ground become bonded from within the floating circuit pathway as to when the house current is restored? Does that cause a distortion to the isolation transformer? If, 1) Only the sub panel breaker is switched off. 2) The Main panel is switched off. 3) The disconnect from the utility is used to cut off from the Main.

Thanks in advance for your help and considerations.

Leyden Jar

 

[LarryFine]

1) Simply, toggle off the 60 amp breaker to sub panel in Main. 2) Switch the Main panel to off. 3) Disconnect from the utility by switching off emergency cut off switch below the meter and above the 100 amp outside service entrance to the Main panel.

I'm not seeing a proper isolation interlock in your description. You shouldn't have to turn off any breakers in a proper transfer switch installation.

Code and law require that it be physically impossible for the utility supply and your back-up supply to ever be connected together, even if you tried to do so on purpose.

 

[zbang]

I'm not seeing a proper isolation interlock in your description. You shouldn't have to turn off any breakers in a proper transfer switch installation.

The transfer switch mentioned seems to qualify for that. The FAQ also contains the note- "Additionally, AFCI and GFCI breakers cannot be used with the Universal Transfer Switches (UTS) because the UTS shares a neutral for all the circuits within it and may cause problems with those types of breakers. " which says to me "2-pole switch".

Otherwise, I'm not following what the OP is doing. If the only difference from the usual ATS practice is an isolation transformer in place of a generator, I don't see a problem other than any required protection for the transformer and it's wiring.

 

[suemarkp]

I wish these transfer switch manufacturers were more upfront with how their switches work. In going to the link for that APC switch, it is a hard neutral transfer switch. I wish they would tell you that and put in bold letters FLOATING NEUTRAL STANDBY POWER SOURCE REQUIRED and give you the sticker you need to put on it too.

I'd suggest either finding a different transfer switch that switches the neutral, or find an alternative power source that is unbonded. Usually, it is easy to unbond the standby power source, but you aren't saying what that source is.

I'm not sure an isolation transformer is allowed for what you want to do. Premises systems usually need to be grounded, so you're going to have a bonding jumper somewhere.

 

[Dennis Alwon]

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