I'm looking at this Reliance Controls transfer switch. I certainly won't buy it and don't recommend one, but the huge hank of wires going from switch to panel only has one neutral wire in it.

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How is this legal under NEC?

Now first I see where the conduit is less than 2 feet, so they don't have a conduit-fill derate on those wires. OK, I buy that.

The generator power comes into this box. There are 10 blacks and 10 reds, 2 wires per circuit switched, so obviously for each circuit, "line" goes to the utility-side breaker and "load" goes to the branch circuit "hot". In utility mode power is taken from "line" and sent to the circuit on "load". In generator mode, power is taken off the generator, sent to the circuit on "load" and returned via that one single neutral.

But it's obvious neutral is not being switched at all. All generator imbalance load for all circuits gets carried on that single white wire.

How can that be NEC legal? Is there a section of NEC that authorizes this style of use?

How well will this work with AFCI and GFCI breakers?

  • this is the install doc .... it says that the device is UL tested ..... images-na.ssl-images-amazon.com/images/I/81zUSrCBzmL.pdf – jsotola Jul 18 '18 at 7:58
  • You know it took me a while studying the installation diagram to understand the concern... Any specifications on the gauge of the neutral? – The Evil Greebo Jul 18 '18 at 12:36
  • My Automatic Transfer Switch(not from this manufacturer) included a nuteral wire for each of the 10 single pole breakers, as well as a Hot wire a well. Is this one a manual transfer switch? – Limo DRIVER Jul 18 '18 at 15:32
  • Only the hot is switched the neutral is for the gauges they use a spdt switch with the hot going to the panel and the generator hot on the other side and the common hot going to the load so there is no way it can backfired thus the mass of wires 3 for each circuit the neutral is not switched so it is not considered a seperatly derived system. – Ed Beal Jul 19 '18 at 14:20

TL;DR: The lack of a switched neutral here has effects on other parts of the system

The presence of a single neutral wire here (which is carrying generator imbalance and providing a 0V point for the wattmeters) means that the generator is relying on the neutral bond in the panel, instead of providing its own. This is important because many portable generators actually come with a neutral bond installed by default (and would need their bond removed to work properly with this transfer switch). Read on for details.

It means your generator is not a separately derived system

There are two basic configurations for wiring a standby generator. Either your generator is a separately derived system, which means it provides its own neutral-to-ground bonding point, or it is not a separately derived system, which means it relies on the house it is plugged/wired into to provide the neutral-to-ground bonding point. This is codified in NEC 702.11, by the way.

Most hardwired generators can be set up either way and left that way without too much difficulty; however, portable generators are pretty much always shipped with their own neutral-to-ground bonding point installed, so they can be safely used as a standalone source of power. Some generator manufacturers provide instructions for pulling that bond for use as a standby generator in a non-separately-derived system, but that means that the bond has to be reinstalled if you ever wish to use that generator for portable power.

But, this fact has ramifications downstream

However, this is not without consequences elsewhere as well. Many interlocked-breaker feeder-type and all select circuit manual transfer switches, as well as panelboard-type breaker interlock setups, do not provide the extra pole needed to switch the neutral between the two bonding points present in a separately derived standby system, limiting their use to non-separately-derived standby systems. On the other hand, double throw safety switches can be readily obtained with the extra pole necessary to switch the neutral; there are interlocked-breaker manual transfer switches with a switched neutral as well, such as the Reliance Panel/Link X series and the Eaton CHGEN series. If you have an automatic transfer switch, note that residential-grade ATSes almost never have a neutral pole of any sort; commercial-grade units are available with a switched neutral pole, but are generally not seen in anything on-topic for this site.

Furthermore, in a non-separately-derived system, all ground and arc fault protection must be downstream of the transfer switch. This is problematic both at small scales, as some portable generators provide ground-fault protection on both their branch-circuit and their power receptacles and also because it means that ground and arc fault breakers have to be shuffled to a standby subpanel from the panel supplying the utility feeders (or can't be used at all in the case of a select circuit transfer switch), and at large scales, where it interferes with feeder/service equipment ground fault protection on high-current, three-phase, wye-connected feeders and services.

On the flip side, the fact the neutral is broken during the switching process can lead to concerns about voltage spikes with separately derived standby systems; as a result, some switching neutral transfer switches have features to overcome this -- either an overlapped neutral (commonly seen on higher end automatic transfer switches), or a sequentially switched neutral (typically seen on manual transfer switches designed with a dedicated switched neutral pole, such as the Panel/Link X series).

  • As far as separately derived and non separately derived systems go, I do not see that as relevant. All that unit is is one big switching device and switches do not need a neutral. It's probably only there to measure the load. – Kris Jul 19 '18 at 2:14
  • @Kris -- a transfer switch for a separately derived standby system must switch the neutral, to avoid putting the two neutral-ground bonding points present in parallel with each other. – ThreePhaseEel Jul 19 '18 at 2:16
  • Yeah I know, but that unit is not switching any neutrals, so not relevant. – Kris Jul 19 '18 at 2:17
  • @kris -- the fact it's not switching any neutrals means that there can't be a neutral-ground bond at the generator, or else you'd have two neutral-ground bonds in parallel with all the perils associated with that! – ThreePhaseEel Jul 19 '18 at 2:20
  • Thank you @ThreePhaseEel I see the error in my thinking – Kris Jul 20 '18 at 17:49

Update on my answer: the neutral is rated for the maximum load permitted by the device. In which case this device has a certain Inlet where it may be 30 amp Max. When the neutral is properly balanced it will have very little current on it.

  • 1
    So your neutral would still be in main panel, connected to gfci/afci circuit breakers If you use them. I get it now, since the Reliance control is only a switch(with no breakers) no neutrals are needed. My Generac Ats has 16 circuit breakers in it, so it needs to not only bring the hot, but also the neturals from the main panel – Limo DRIVER Jul 19 '18 at 15:50
  • in the directions it tells you existing circuits that are on GFCI and afc breakeeii will not work – Kris Jul 20 '18 at 17:52

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