There problem with unknown systems is unknown fault currents and duration ! That may sound trite, but it is key. There is a huge difference between the maximum flash you can possibly face downstream of a 13A fuse, vs a 100fuse, vs a 400A slow blow one.

(but you can estimate - assume I2t * half the supply voltage is the energy available to create the bang, the other half of the supply voltage going in the supply internal impedance, and imagine that energy spread out over a sphere with the fault at centre - as the outer surface area of the sphere is 4.pi.r^2 you can quickly get to joules per square cm. About 5 of those on bare skin is enough for an instant painful sun-tan and much more gets you into into hospital trips and by about ten times that on large areas of the body means effects you don't recover from.)This sets a safe distance of closest approach for bare skin.

There are also non-flash arc effects, like being basted in droplets of molten metal, that can make the scope for injury from accidents like spanner slipping between the phases suddenly far greater. Meanwhile rated light coloured cotton overalls, and certainly long sleeved tops of the right materials are so cheap that not having that would almost be reckless and already make a huge difference by reducing how much body is exposed.

Having the mentality of deciding at the outset, this is just a goggles and gloves job, or this a  visor and gauntlets job or this is a use a pointy stick job and doing that grading as a dynamic process may help.  PPE is something you need to have the habit of selecting at the outset, not 'oh I'll go and get it if  I need it."

The trick then maybe to get good at looking at something and deciding what the level of risk is.  Simply put the problem is one of total fault energy, as above, times a focussing factor that depends on the enclosure - you may get energy reflected off the back and sides of a box in a way that makes having your body near the open front  2 or 3 more dangerous than if the fault was dangling in free space - the effect is that the enclosure protects the  things behind and to the sides from the exposure, but does that at the expense, at least partly, by redirecting that blast of energy that would have gone that way forwards instead.

M.

There problem with unknown systems is unknown fault currents and duration ! That may sound trite, but it is key. There is a huge difference between the maximum flash you can possibly face downstream of a 13A fuse, vs a 100fuse, vs a 400A slow blow one.

(but you can estimate - assume I2t * half the supply voltage is the energy available to create the bang, the other half of the supply voltage going in the supply internal impedance, and imagine that energy spread out over a sphere with the fault at centre - as the outer surface area of the sphere is 4.pi.r^2 you can quickly get to joules per square cm. About 5 of those on bare skin is enough for an instant painful sun-tan and much more gets you into into hospital trips and by about ten times that on large areas of the body means effects you don't recover from.)This sets a safe distance of closest approach for bare skin.

There are also non-flash arc effects, like being basted in droplets of molten metal, that can make the scope for injury from accidents like spanner slipping between the phases suddenly far greater. Meanwhile rated light coloured cotton overalls, and certainly long sleeved tops of the right materials are so cheap that not having that would almost be reckless and already make a huge difference by reducing how much body is exposed.

Having the mentality of deciding at the outset, this is just a goggles and gloves job, or this a  visor and gauntlets job or this is a use a pointy stick job and doing that grading as a dynamic process may help.  PPE is something you need to have the habit of selecting at the outset, not 'oh I'll go and get it if  I need it."

The trick then maybe to get good at looking at something and deciding what the level of risk is.  Simply put the problem is one of total fault energy, as above, times a focussing factor that depends on the enclosure - you may get energy reflected off the back and sides of a box in a way that makes having your body near the open front  2 or 3 more dangerous than if the fault was dangling in free space - the effect is that the enclosure protects the  things behind and to the sides from the exposure, but does that at the expense, at least partly, by redirecting that blast of energy that would have gone that way forwards instead.

M.