I'm getting ready to move some hardware into a new datacenter location and that includes two mikrotik devices that use wall warts. I will only have access to 208 volt phase to phase power, no neutral, no 120volt. Looking for suggestions/experience, my not quite happy with it semi kludge of a first instinct is to use c13/c14 to nema 5-15p adapters after triple checking the voltage range on the supplies to ensure they are universal supplies whose voltage range includes 208 volts. Finding an affordable external 24 volt supply that takes a c13/14 input at 208 volts isn't something I expect to be easy and a little initial googling seems to back that up and I expect anything home grown/wired will get a very hard rejection for safety reasons (I know I would in their shoes in that situation). Even in a locked down location in a restricted access setting I don't like ending up with a plug at a voltage it isn't normally used at just in case someone later doesn't know and tries to plug something else in (no one else is currently expected to be authorized to plug anything in, but ...). I also wanted to check on peoples experience and advice regarding how much I should worry about grounding the ground screws and if I should worry that both legs of the power supply being hot instead of one being a grounded neutral conductor will create some other issue beyond the change in voltage.

I've done a lot of setups over time, and dealt with a fair bit of the fairly minor electrical things (installing control relay packs on circuits, replacing outlets, etc.) and done specifications for other more significant work (like number of circuits and outlet locations, etc. needed to provide power for new cubicles, copiers, and on-site mini server closets), but this is my first time in a 208 single phase setup and the first time this has come up. I'm actually somewhat familiar with 208 3 phase and even a bit with 277 single phase and 480 3 phase, though most of the things I deal with are 120 volts.

So, any advice on problems I've missed in my kludge option, or even better recommendations for a better way to handle it safely and how much I should worry about getting a ground to those ground screw terminals?

Unfortunately 120 volt power from the datacenter isn't an option in this case, and the provided power does not have a neutral, so the fact that the 208v legs would be 120v to neutral does not help me. This is a datacenter environment, so power is expected to be very, very clean and I'm not expecting any issues with high amounts of static electricity or with electrical shocks entering data ports, and I expect the rack is well bonded with ground, if that was different I'd definitely need to be rigorous on my grounding of the ground screws in the back (and I've dealt with bad power situations, high static locations, external copper with high risk for shock, and other variations of situations where I've had to be extremely aggressive with grounding, bonding, and surge protection, someday I'll post some of that story).


Edit: I should add I'm pretty handy with electronics, but I'm not interested in opening these up and hacking in a new internal power supply instead of using the wall wort or possibly a different external power supply.

Aren't most power bricks have an c13/14 and auto-switching 90-240VAC?

Actually for the typical input configuration of a swichmode powersupply it is better to have symmetrical input than unbalanced (one lead at ~gnd and the other at rated voltage).
And indeed, 208 volt would be perfectly within the bounds of the typical power supply we use here on our 220-240VAC line voltage.
A supply rated for 90-240VAC should just work. 208 volts may be uncomfortable for you but here in Europe we have 230V everywhere and we are still alive.

The important issue when operating in such an environment is usually more that power bricks are physically inconvenient to have.
It would be welcome when more equipment came with a c13/c14 input rather than a DC input and a power brick.
Some of the older devices (e.g. RB2011 in rackmount case) can be converted (they have a lot of empty space and a cutout for a c14 socket).

Mada3k:

I'm not sure why I was forgetting that, if your referring to things like https://mikrotik.com/product/24HPOW maybe because once I'd tried googling and not seen it combined with my head focusing on wall wart or rack mount instead of inline supplies, and of course since they have the cable included they usually don't state things like c13 or c14 in the description and so don't show up in Google in my search for them. The included supply I have is 24 volt and a is a us plug but in the style of https://mikrotik.com/product/18POW . I'm feeling a little silly now given that I've actually swapped out a lot of inline power supplies to use color coded c13/c14 extension cords and c13/c14 splitters and distribution boxes a fair bit recently to better manage a vs b vs single fed IT load vs single fed security related loads, etc. and that's even where my familiarity with the adapters to plug a 5-15p into one of those cords comes from.

Well one problem solved, thanks.

Now on to the rest, like any concern over a dual hot leg, not hot and neutral. I don't know enough about power in countries that use 220 to know if that's usually two hot legs or a hot and a neutral (grounded but current carrying, separate from protective earth/ground wire, but bonded to it in the main panel). Given it should be an isolated power supply I would not expect issues, but I've seen enough to know to not assume. Also how worried I should be about making sure I bond grounds on the back of the equipment (things like a rb3011 that's a secondary/backup router, the primary is a much larger x86 system with multiple 10ge ports, but even if it's a lot slower than the primary I wanted some redundancy in place) keeping in mind a very well controlled/regulated/protected power supply, temperature, humidity, and well bonded racks, so in a very low risk of odd power spikes, surges, and static build up. I'm planning to do it if it's easy to be safe, but I'm not sure how easy it will be to get a good point to ground to in this location most likely my best available point will be the ground terminal on my pdu connected to the ground in the whip feeding me power. (I have other locations which much more significant grounding arrangements like a dedicated ground straight to the main building ground rods for use with surge suppressor systems or large dedicated isolated ground wire to the main 120/208 panel after the transformer, which is bonded to the master bus bar a few feet away).

Pe1chl:

I'm not uncomfortable with 208, just haven't used it in this context much, and never dealt with needing to get small switch mode power supplies onto it where the one I start with is made with a different plug.

I've dealt with 208 3 phase and 480 3 phase in some fairly large systems (like 10 ton ac units drawing dozens of amps per phase, and large industrial battery chargers [ when you have 48 volt 200 amp output, chargers get a bit different, I actually see them in 480 3 phase more often]), I'm well aware of it's safety when done right and it's benefits, and all the things with c13/14 connectors are going to be easy, which is about 9 of the 11 power connections I need to make, it was just adapting the power supplies where I started with 120 volt plugs on them that made me have to think. For instance if the electronic components were fine but perhaps the 120 volt plug might have had an issue if I'd just forced 208 into it (unlikely, but possible), and the balanced vs unbalanced power, when a place I work with lost its neutral bond from one transformer and neutral was floating relative to ground, most things were fine, but a few things reacted very badly to having 120 "neutral" to ground, 120 "neutral" to hot, and 208 hot to ground, which is not that different from a 208 volt phase to phase setup. As I work through it with posting this I'm realizing without a ground on the supply input that it's much harder for that to create an issue, but while I deal with a fair bit of electrical stuff in some fairly odd situations, I'm very well aware that if you're not sure what to do in a situation you check first, knowing the limits of what you know and realizing when you don't know something is key with electricity and the only way to deal with it safely.

While I'm pretty sure a full bridge rectifier would not care much, I'm pretty sure a half bridge rectifier that cut components by assuming a constant neutral as one leg could get badly screwed by a balanced power supply as an example.


But in any event the power supply issue is solved with the external bricks, they are a pain, but less than the wall worts would have been and at the moment the rack will be about 3/4 empty so the space won't be an issue (and if someone needs some hosting in Ashburn, let me know, I've got a lot of spare capacity at the moment once this goes live both in terms of space and power for colo and in terms of capacity on the virtualization hosts I'm installing)

In Europe the power is 230V AC asymmetric (one side is ~gnd the other is 230V AC) and the next step up is 3-phase 230/400V AC.
I.e. you have 3 230V AC circuits like the above, with 400V between the phases. This is the low voltage setup commonly available in domestic and small industrial environments.
We never use 2-phase setups here.

But the input of a SMPS normally is completely floating and symmetrical, except that it has a capacitor between each line input terminal and the ground terminal.
Here in (continental) Europe plugs are not polarized so a powersupply with C14 input would not know beforehand which pin is neutral and which is hot.
With asymmetric supply that unfortunately means that when the ground is not connected, it floats at half the supply voltage (115V) and this can cause surprise shocks and damage to equipment.
But when the input is symmetric, that isssue does not occur. That is why I wrote "for the typical input configuration of a swichmode powersupply it is better to have symmetrical input".

I would not be worried and just plug it in, maybe with some warning label to prevent people from quickly removing the C13 connector from your powerbrick and connect it to their equipment they brought, and which expects 115V. Although in the computing world there is less and less equipment that would not just work OK on 208V or above.

In Europe the power is 230V AC asymmetric (one side is ~gnd the other is 230V AC) and the next step up is 3-phase 230/400V AC.
I.e. you have 3 230V AC circuits like the above, with 400V between the phases. This is the low voltage setup commonly available in domestic and small industrial environments.
We never use 2-phase setups here.

That is not completely true. In The Netherlands there are still some 3x230V networks (230V between phases, no neutral). Also in Belgium it is a lot more common. Wikipedia just told me that in Norway this is very common.

In Europe the power is 230V AC asymmetric (one side is ~gnd the other is 230V AC) and the next step up is 3-phase 230/400V AC.
I.e. you have 3 230V AC circuits like the above, with 400V between the phases. This is the low voltage setup commonly available in domestic and small industrial environments.
We never use 2-phase setups here.

But the input of a SMPS normally is completely floating and symmetrical, except that it has a capacitor between each line input terminal and the ground terminal.
Here in (continental) Europe plugs are not polarized so a powersupply with C14 input would not know beforehand which pin is neutral and which is hot.
With asymmetric supply that unfortunately means that when the ground is not connected, it floats at half the supply voltage (115V) and this can cause surprise shocks and damage to equipment.
But when the input is symmetric, that isssue does not occur. That is why I wrote "for the typical input configuration of a swichmode powersupply it is better to have symmetrical input".

I would not be worried and just plug it in, maybe with some warning label to prevent people from quickly removing the C13 connector from your powerbrick and connect it to their equipment they brought, and which expects 115V. Although in the computing world there is less and less equipment that would not just work OK on 208V or above.

I'll be swapping to the inline supplies with the c13/14 connections probably just for piece of mind and easy of strapping down, but I'm now pretty sure my original adapter idea would have been manageable, and will be a temporary backup if the new supplies don't come in time.

For reference for those outside the us or just unfamiliar, the US has 3 dominant forms of power, and none of them is 2 phase, I'll avoid going into the less common forms (certain odd voltages and transformer arrangements used largely in old large industrial settings but also sometimes elsewhere, one of which actually is 2 phase power, but that's very, very rare).

Mid-large commercial power, including at some points inside datacenters, is 480 three phase, which is 277 phase to neutral, it's used extensively for larger loads in businesses (hvac, etc.) and often lighting runs on 277, it's also often used for motors over a few horsepower (one hp is ~750 watts or 0.75kw for those who rate motors that way). businesses often receive their power this way

Smaller businesses may have a 208 volt 3 phase feed, and larger ones will have transformer(s) to step down the 480 to this to power smaller loads and outlets, etc. 208 phase to phase in 3 phase makes 120 phase to neutral, most 240volt home gear can also run on 208 (using only 2 of the three phases), but resistive heaters don't create as much heat, so you need to account for that in sizing things like water heaters.

Homes and really small business mostly run on split-phase 120/240, it's not really 2 phase power, though some things are phrased as if it was, it's actually a single phase with a center tapped transformer, so one end is 1 "phase", the middle is the neutral, and the other end is the other "phase", with 120 volts "phase" to neutral, and 240 "phase" to "phase", each leg is 180 degrees out of phase with the other, where in 3 phase systems they would be 120 degrees apart. Most homes run almost entirely on 120, except certain large appliances like electric dryers, electric ovens, electric hot water heaters, air conditioning, heat pumps, and dedicated electric vehicle charging setups. Motors running on single phase need help starting and sometimes running as there isn't a rotating magnetic field naturally the way there is with multi phase systems (even 2 phases 90 degrees away from each other, which actually did exist for a while and sees some lingering historic use because rewiring large old buildings is expensive), typically they use a capacitor to generate the additional windings current. Motors running on multi phase systems also deliver more constant power output and better efficiency.

Have you considered using PoE from a switch to power them? Most of the devices that take AC power via adapter seem to also take PoE in on at least one port.

A proper (and legal) switched power supply should not have any required specific hot or neutral leg.

For reference for those outside the us or just unfamiliar, the US has 3 dominant forms of power, and none of them is 2 phase, I'll avoid going into the less common forms (certain odd voltages and transformer arrangements used largely in old large industrial settings but also sometimes elsewhere, one of which actually is 2 phase power, but that's very, very rare).

Homes and really small business mostly run on split-phase 120/240, it's not really 2 phase power, though some things are phrased as if it was, it's actually a single phase with a center tapped transformer, so one end is 1 "phase", the middle is the neutral, and the other end is the other "phase", with 120 volts "phase" to neutral, and 240 "phase" to "phase", each leg is 180 degrees out of phase with the other, where in 3 phase systems they would be 120 degrees apart.

This is what I referred to as 2 phase, apparently it should be called split-phase (it seems to me like a 2-phase 180 degrees system, similar to 3-phase with 120 degrees: angle = 360 / n.phases.
That is what we never use here. It is either single phase or 3 phase. And normally it is unbalanced, I heard the folklore about 3x230V networks that should be in some old city centers, but I never encountered such a system and you will certainly never find it in something as modern as a datacenter.

This is what I referred to as 2 phase, apparently it should be called split-phase (it seems to me like a 2-phase 180 degrees system, similar to 3-phase with 120 degrees: angle = 360 / n.phases.

To distinguish it from 2-phase with a 90 degree phase angle which can be used to drive motors without a start/run capacitor, not very common these days. You can convert between 2-phase (0/90 degrees) and 3-phase (0/120/240 degrees) with a Scott-T transformer.

I heard the folklore about 3x230V networks that should be in some old city centers, but I never encountered such a system and you will certainly never find it in something as modern as a datacenter.

Except that is what the OP has in their datacentre, albeit 3x208V rather than 3x230V. Raritan have a useful document https://www.raritan.com/assets/ram/reso ... Power_.pdf with page 7 discussing the pecularities of North American wiring where you may have PDUs connected with 3P+N+E and a mix of 208/120V outlets, or 3P+E for 208V outlets only.

I heard the folklore about 3x230V networks that should be in some old city centers, but I never encountered such a system and you will certainly never find it in something as modern as a datacenter.

Except that is what the OP has in their datacentre, albeit 3x208V rather than 3x230V. Raritan have a useful document https://www.raritan.com/assets/ram/reso ... Power_.pdf with page 7 discussing the pecularities of North American wiring where you may have PDUs connected with 3P+N+E and a mix of 208/120V outlets, or 3P+E for 208V outlets only.

Well I was referring to the situation here, where 3x400 is normal (with 230 between phase and neutral). The single-phase sockets have N and one phase, and thus have unbalanced voltage.
In some very old networks there is supposed to be that 3x230 system but I think in most cases it already has been mostly replaced by installing a 3x400 cable and put all new connections on that.
(not in Belgium and Norway, apparently)

A weakness of the 3P+N system is that in case of a failure of the N wire somewhere between the network and a building installation, the voltages on the 3 phases become unpredictable and will depend on loading of each phase. We had a case where this happened in one of our offices and tens of PCs power supplies smoked out due to the voltage rising towards 400V (don't know how high it actually went but the powersupplies released the magic smoke).
That cannot happen in a 3x230 network (or similar a 3x208 network in your case).