Re: [EE} Protecting CAN bus

Disbelieved by some:

Place a single turn loop, maybe around 300 millimeter diameter,  in the
cable at ground level where it enters the building.
Lightning apparently doesn't go around corners - even though calculations
suggest the impedance is far too low to be significant.
Lightning will blow through the insulation to ground somewhere on the loop
if a strike is severe enough.


        Russell

On Sat, Jun 28, 2025, 10:37 PM Sean Breheny <[email protected]> wrote:

> There are specialized TVS diodes meant for use with CAN. One I've used
> before is the PESD1CAN,215 from Nexperian. They have lower than typical
> capacitance to avoid affecting the signal.
>
> I would put these TVSes on each node.
>
> Do you have termination resistors at each end of the cable?
>
> I assume that you have a "ground" reference wire in the cable as well to
> make sure that the common mode voltage at each node isn't too large?
>
> I would say that any time you have wires of significant length entering
> your house there should be lightning protection directly to a ground rod
> right before the point of entry to the house. This should probably be gas
> discharge tubes to be able to handle much greater current than TVSes. You
> would think that the risk would be non-existent since the wires are running
> close to the ground but that's not true. A lightning strike anywhere near
> those wires could cause momentary potential differences of thousands of
> volts between those lines and the local ground.
>
> Sean
>
>
> On Fri, Jun 27, 2025 at 1:35 PM David C Brown <[email protected]> wrote:
>
> > I am using a CAN bus with MC2562 drivers for a home control system.
> > This allows a unit in my hall to monitor and control various things in my
> > garage:  car door, pedestrian door, lights, alarm.
> > The garage is some 50 meters from the house and I use CAT5 cable running
> in
> > conduit at ground level for the bus.
> >
> > Naturally I am concerned about lightning and other nasties so I am
> fitting
> > a bidirectional TVS diode on each side of the bus.
> > My question is:  do I need those diodes on every device connected to the
> > bus or is it sufficient to fit them only on the two units at each end?
> > I ask because I have a suspicion that putting more TVS diodes on the line
> > is degrading the signal
> >
> >
> > __________________________________________
> > David C Brown
> > 43 Bings Road
> > Whaley Bridge
> > High Peak                           Phone: 01663 733236
> > Derbyshire                eMail: [email protected]
> > SK23 7ND          web: www.bings-knowle.co.uk/dcb
> > <http://www.jb.man.ac.uk/~dcb>
> >
> >
> >
> > *Sent from my etch-a-sketch*
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