Hi there

I'm in a project that requires the assembly of an enclosure with several electronic devices. The input voltage is 230VAC and the devices work at 12 VDC so a power supply is needed inside of the enclosure. The enclosure comes with a metal plate that should be fixed to the box with screws, but for our project we need to have two levels/floors, since all the devices can't fit in one floor. We decided to use metal spacers that will divide the plates. Some devices (PCBs) are screwed to the plates using also metal spacers.
We are using a meanwell RS 75-12 power supply whose body is made of metal (chassi). The bottom of the power supply is screwed directly to the metal plate. The line, neutral and earth wires enter on the enclosure through a cable attached to an external connector. Internally each wire is screwed on the respective terminals.
My doubts are the following:
- Is the chassi of the power supply connected to the earth terminal?
- In case of a lightning strike on the enclosure, will the devices be safe?

By my understanding, the earth wire is mainly used to prevent electric shocks to people, in case a wire is somehow connected to the body of the device.
But what happens in a lightning strike? The enclosure is to be put in a tower (outside). Shouldn't high voltage be directed to earth terminal? Do I need to attach a cable between the earth terminal and the enclosure?
Not sure if I explained this in a clear way. If you need more information or clarification just ask

Thank you!

 

But what happens in a lightning strike?

The effects can be quite unpredictable, but with a direct strike it's possible the whole enclosure could melt and the contents would likely be ruined by excessive voltage. Mother Nature is unforgiving.

 

The effects can be quite unpredictable, but with a direct strike it's possible the whole enclosure could melt and the contents would likely be ruined by excessive voltage. Mother Nature is unforgiving.

Hmm, so basically, doesn't matter how the wiring is made, the devices will be destroyed. Ok, what if the lighting strike hits, lets say the tower instead of the enclosure? Could the electromagnetic field cause the box to have, lets say energy that somehow damage the components? Because if not we can put a lightning rod on the tower.
All this doubts arose when our partner created a similar enclosure, and they said that all elements need to be connected by earth, to the chassi of the box to avoid damage. The chassi was connected to earth terminal in the power supply. However, there was no connection to earth that exited the box.

 

Hi there

I'm in a project that requires the assembly of an enclosure with several electronic devices. The input voltage is 230VAC and the devices work at 12 VDC so a power supply is needed inside of the enclosure. The enclosure comes with a metal plate that should be fixed to the box with screws, but for our project we need to have two levels/floors, since all the devices can't fit in one floor. We decided to use metal spacers that will divide the plates. Some devices (PCBs) are screwed to the plates using also metal spacers.
We are using a meanwell RS 75-12 power supply whose body is made of metal (chassi). The bottom of the power supply is screwed directly to the metal plate. The line, neutral and earth wires enter on the enclosure through a cable attached to an external connector. Internally each wire is screwed on the respective terminals.
My doubts are the following:
- Is the chassi of the power supply connected to the earth terminal?
- In case of a lightning strike on the enclosure, will the devices be safe?

By my understanding, the earth wire is mainly used to prevent electric shocks to people, in case a wire is somehow connected to the body of the device.
But what happens in a lightning strike? The enclosure is to be put in a tower (outside). Shouldn't high voltage be directed to earth terminal? Do I need to attach a cable between the earth terminal and the enclosure?
Not sure if I explained this in a clear way. If you need more information or clarification just ask

Thank you!

My experience with a lightning strike was that one device, a monitor radio, had the front blown off and most of te individual components destroyed electrically. The other device, which the radio was sitting on, a Kenwood TR2600, was not damaged.
In the TS case, it seems that the enclosure is plastic of some kind, with a metal mounting plate inside. And a mains power feed enters from below. A lighting strike will fry the power supply as the lightning jumps to the mains wires. Put the other electronics in metal boxes well grounded to the metal plates all well connected to each other. It might survive.

 

Hmm, so basically, doesn't matter how the wiring is made, the devices will be destroyed. Ok, what if the lighting strike hits, lets say the tower instead of the enclosure? Could the electromagnetic field cause the box to have, lets say energy that somehow damage the components? Because if not we can put a lightning rod on the tower.
All this doubts arose when our partner created a similar enclosure, and they said that all elements need to be connected by earth, to the chassi of the box to avoid damage. The chassi was connected to earth terminal in the power supply. However, there was no connection to earth that exited the box.

It's possible but not easy to make things direct strike 'resistant'. We had direct strikes on the ships mast at sea frequently with no damage to the internals of a properly engineered shielded and grounded enclosure near the strike but these things were also designed to work after a nuclear EMP blast.

 

Nsaspook;
I once was fortunate enough to visit a Naval laboratory in Philly which validated electrical and electronic equipment for use onboard ships.
Much of what was there was classified, and we could not loiter and peek. But I do recall seeing the heaviest grounding straps ever.

 

Nsaspook;
I once was fortunate enough to visit a Naval laboratory in Philly which validated electrical and electronic equipment for use onboard ships.
Much of what was there was classified, and we could not loiter and peek. But I do recall seeing the heaviest grounding straps ever.

PolyPhaser Grounding.


When you know you will get hit, you wear protection and it's like the martial arts of redirection mainly with lightning. Karate, force meets force, Aikido, force redirects force, and Judo, force accelerates force.
Make it much more likely the bolt will hit something other than your gear.

https://www.bicsi.org/uploadedfiles/PDFs/conference/2020/winter/CONCSES_5C.pdf

What can we do to reduce, or even eliminate, damage to our electronics? 
GOAL: Keep as much of the energy outside the building/hut/enclosure as practical/possible and AWAY from the electronics! 
How? Reduce Inductance 
Lightning really takes the path of least inductance – not the path of least resistance. 
Let’s first assume that the soil is a perfect ground. 
Let’s assume the lighting only hits the lightning rods 
If we can get the energy down to the soil, instead of into the electronics, everything will work out fine. (This is mostly true)

 

Lightning really takes the path of least inductance – not the path of least resistance

So loop the power feed a few times to add inductance and bypass the whole thing with a lightning rod and massive straight cable to a hefty ground rod?

 

The problem develops when a few thousand amps pass thru perhaps one ohm of resistance between tower top and bottom, and a few thousand volts appear across that tower.

 

A looong time ago I worked on a communication system intended for the back of a Landrover and it had wires to be clipped onto phone lines. It was intended to be useful after a NEMP event. This thing was built in a cast metal box with separate internal sections. The external connections went into one of the smaller inside sections and the signals were passed into the internal sections via fibre optics. When disaster happened the small interface boards would be fried but were easily replaced to get box working again. I don't know how well the Landrover or personnel would survive the event.

 

Did some reading, apparently lightning rods are useless on metal towers because the tower itself is such s good conductor. The solution is massive grounding. Broadcast towers apparently suffer strikes every time a storm goes by without damage.

 

So loop the power feed a few times to add inductance and bypass the whole thing with a lightning rod and massive straight cable to a hefty ground rod?

If only it was that simple.

https://cryptome.org/eyeball/nsgah-eyeball.htm

https://www.navy-radio.com/frd10.htm

 

Did some reading, apparently lightning rods are useless on metal towers because the tower itself is such s good conductor. The solution is massive grounding. Broadcast towers apparently suffer strikes every time a storm goes by without damage.

My 58 foot tower was not damaged by a direct hit. But the RINGO antenna was mostly evaporated, Like the Diamond X500 was during an earlier direct hit. The tower is quite well grounded. 3/0 ground wire on each leg, into 8 ft copper pipe ground rods.