I’m installing a 450m AP using a non-penetrating roof mount. The DC wiring and CAT5 wires come up through the attic to the roof. Since this isn’t a traditional tower where the mast is used as ground, what ways can I ground this? Should I bother installing the LPU right at the base of the mast (it’s 5 feet tall)? Should I place another LPU right inside the attic or should I place the 2nd one where the DC wires terminate at the power supplies (in the basement of the building)?
Hello Ryan, Welcome to the Cambium community!
The major reason for grounding is to protect the building and occupants from outside energy getting into the building. Secondary point is to protect the equipment, and hopefully, both happen at the same time. The electrical code for your state/province/region governs what you need to do.
The electrical code for both Canada and the US says that you have to protect the building from any stray energy conducted along any cable entry into the building - if I remember its in chapter 55 of the Canada Electrical Code (I’m in Canada). At any rate, LPU should be placed outside of the roof, not in the attic. The base of the mast is the right location. Also, the radio should be grounded to that ground, and you may need to run a separate ground riser and ground rod to properly meet the electrical code standards. If you have a ground bus in the basement, you could certainly put the 2nd DC LPU there, but it would not serve a significant purpose for protecting the building, just your own power supply.
A mast is a mast 5 feet or 50 feet and treat them the same.
I use two surge suppressors one at the radio and one right before entry into the building.
I use separate #8 wire for each of the surge suppressors to connect to main service ground. If it is a long distance away I often drive a second grounding rod and connect it to the main service ground using #6 wire or larger. I then connect the two #8 wires to the second grounding rod.
I attach a five foot copper pipe w/ crimped point to the top of my masts then connect to main service grounding rod using #6 wire.
An update of sorts. Experienced a terrible lighting storm last night. It began with little to no rain with frequent, close proximity lightning strikes. Think SciFi movie special effects.
The storm tripped a GFI, blew out a couple LED lightbulbs in the kitchen a fried a gas leak sensor in the basement an 8 port switch and a smart switch for my garage lights. I was sure the radio was toast.
But thanks to God, grounding efforts and sturdy Cambium gear the link is still functioning.
Not that it will help now, but you should consider a whole house surge arrestor to be added to your electrical panel. What you described is classic surge on the power lines entering your house (you have good grounding so will be vulnerable to sharing the surge). Unfortunately these things also get cooked often and need replacement but its better than replacing all your appliances!
Availability and locality approvals are a bit of a mess, talk to your local electrician.
There are only two types that I consider for install: MOV and gas discharge. Both should be installed together.
MOV is a voltage clamping device that produces heat (can produce a lot of heat, so dont install neat combustables) when clamping the voltage. Get a type with quick change units, they are more expensive up front but you dont need an electrian to swap them out later.
Gas discharge is a high current device that protects your equipment from being the best path to ground. Essentially they are 130v neon tubes and they direct large current surges to ground. Usually have a life of 10 to 20yrs depending on how active your area is for lightning strikes. These do get warm when a surge happens but not usually hot enough to cause issues.