A better analogy I often use is a Newtons cradle with the middle 3 balls being the conductor the outside balls being the input and output forces EMF/Current. It is NOT a complete analogy very few analogies in Physics related actions or observations are.
one
My issue is many people obviously have little real world experience outside of a lab, giving rise to recalling the line
"for spherical horses in a vacuum"
Lets first look at the potential LEGAL issues in the UK
1/ A church would have to have fixed electrical work carried out by a 'competent person' who is a member of one of the electrical contractors bodies (NOT the IET). Who has all the regular certifications and necessary recertification certificates. To comply with law and buildings and probably public liability insurance.A 'competent person' is NOT someone with only academic qualifications in electronics or the like.
Similar problems exist in other countries.
2/ A church would be deemed commercial or industrial grade electrics not the same as domestic wiring as it is not a 'dwelling' and more likely deemed a public place.3/ A 60ft (approx 18.3m) run as fixed wiring on twin and earth would need to be on a fused or RCD spur/radial circuit. Also clipped more often then every meter, or held in trunking/conduit.
If run as an extension lead every so often the Church has to perform Portable Appliance Tests on the lead and equipment.
4/ Run as fixed wiring (or extension lead) the Building Regulations and Wiring Regulations stipulate that except where unavoidable like short distance pinch points there MUST be separation between power and data/phone or similar wiring. Usually this is around 25 to 30mm.5/ By giving instructions to someone else how to do electrical wiring in rare circumstances, can mean someone may come after you as well if found not to be a 'competent person'.
BTW I deal with electricians regularly and know where I am coming from on this.
Now the NOT exact current in both halves ========================================
All the postulations so far missed a few key words in original that stated things like 'starting with' as in this is NOT the only possible cause.
All the thread drift so far has had the standard physics criteria of
For a perfect source For a ideal cables For a perfect resistive only load For perfect power transfer with precisely matched load to source Within a Faraday cage Possible also within a vacuum
The APPROXIMATE RMS (or average current) for a time period will in real life be APPROXIMATELY the same. The instantaneous is very rarely EXACTLY identical in both conductors.
OTHER (but not exhaustive list) reasons why not EXACTLY the same in the real world -
a) signal injection - having dealt with situations of TV stations, body scanners, X-ray systems, mobile phones.....
It is possible to get signals injected in parts of the circuit which does imbalance the current, sometimes for prolonged periods of time.
b) Supply being non-perfect causing effects from wiring and/or attached equipment. The mains supply is rarely anywhere near a perfect sinusoid, ask anyone who has done any form of UPS type design and testing.
c) Imperfect cable of other faults in wiring.
d) Bad load, where by current is diverted elsewhere by bad design or deliberate design usually to earth or earth wire.
Other injection or diversion effects of the load equipment
e) Infestations and contaminations - insects, animal droppings water ingress etc. apply resistive and/or capacitive loads/diversions of current. Sometimes causing other issues which will degrade the cable INCREASING the cable Earth Leakage Capacitance or DECREASING Earth Leakage Resistance.
I have seen many instances where twisted pair cat5 and phone cables have had faults due to damp, bird droppings etc. causing things like PABX to ring with phantom calls on multiple lines.
f) Delay line effects of the equipment, often neglible or non-existant but has been known.
g) Earth Leakage - every piece of cable and equipment has Earth Leakage For setups like this it will be in (but NOT limited to)
Cable - standard 2.5mm^2 Twin and Earth Leakage Capacitance is of the ORDER of 80-100pF/m
Connection points not giving good return and leakage through equipment to earth or real earth of the building structure One electrician told me of a bad 11kV feed to an establishment having poorly connected Neutral, caused all sorts of issues and heater effects.
Mains Input Filters have capacitors to earth built in
Power supply transformers and circuitry often has inherent earth leakage losses
Other filter capacitors deliberately added in PSU circuit
Contamination see (e).
Note in a belfry and bell tower probably built from stone or brick during wet weather the building structure absorbs moisture RAISING the earth leakage capacitance and/or DECREASING the earth leakage resistance. Thus causing more Earth Leakage Current.
Note having had to deal with medical equipment the equipment has to meet for EN 60101-1 Earth Leakage in the actual earth wire not other extraneous leakage (which is tested for even lower limits).
Normal Conditions 0.5mA Single Fault Condition 1mA
Normal Powers supplies external or built-in for domestic and commercial usage can have earth leakage as high as 10mA.
Please do not say but the RCD/Earth Leakage Circuit Breaker (ELCB) catch these 'fault conditions', actually these conditions will always be there. RCD/ELCB generally have a trip point of APPROX 30mA, which is the when it leaves the factory MINIMUM point any of them will trip some actually with tolerances can be HIGHER.
For a small load like a 60W PSU, the supply current is APPROX 60W /240V approx 250mA, so 10 to 30mA is noticeable.
Many people in domestic wiring have problems due to strange tripping due to variations in Earth Leakage currents, let alone aging faults where they may start tripping at lower levels, or other strange faults where they get locked on, or the internal magnet is degaussed.
There are many causes for REAL WORLD differences compared to theoretical calculations. I am sure there are MANY more that can be found by others, this is NOT a definitive and exhaustive list.