Welcome to ECN!!!
You are among some very knowledgeable People here!
As to the shock:
Like "Hotline1" mentioned, the maximum output of the Transformer's Secondary side would be 30 mA (30 milli-Amps, or 0.03 Amp).
This is what would be available if the Secondary side was Short-Circuited, and an Ammeter was placed in Series with the Secondary's Current (like placed in series with whatever is used to short-circuit the secondary circuit).
Also, as mentioned by "Larry Fine", the Secondaries of Gas Tube Discharge type Transformers are Center Tap Grounded (or "Mid-Point" Grounded).
So if the output of this Transformer was 9 KV (9,000 Volts), the Voltage-To-Ground on the Secondary side will be 4.5 KV (4,500 Volts).
However, the available Short-Circuit Amperes (SCA) will still be 30 mA.
Some Transformers will have "Split Coil" Secondaries - which are two separate Secondary Windings, connected together in Series Additive fashion (the jumper between the two coil ends is tapped; thus creating the Mid-Point tap to Ground), while others will have a physical tap made to a "Full-Length" single Secondary Winding, at a point which is 50% of the entire Coil's Winds (or turns).
Example: 120V Primary x 12,000V Secondary (100:1 winding ratio).
Primary Winding has 500 turns of # 22 AWG Copper wire wound around the Core, and the Secondary has 50,000 turns of # 40 AWG Copper wire wound around the core.
At the 25,000th turn, a Copper wire lead is terminated to the Coil - thus creating a Mid-Point Tap.
OK, enough of that!
The Transformer you were involved with, should have the following ratings:
Primary (Input): 120VAC, 2.25 Amps (270 VA)
Secondary: 9,000VAC, 0.030 Amps (Mid-Point Grounded).
Voltage To Ground - Secondary: 4,500VAC
Since you were connected to the Secondary of this Transformer only, and to only one of the Secondary side's Termination (off one Secondary Bushing), the potential _SHOULD_ only have been 4,500 Volts - plenty high enough to kill!Anything above 50 Volts may be considered lethal
(as the Voltage may be high enough to push a high level of Current)
If the skin is very wet, plus conductive materials are present - like Salt, Chlorine, Iron, etc., Voltages lower than 50 Volts
may allow lethal levels of Current to flow through a Person's body.
If your skin was very dry at the time of the shock, and there was very little to no conductive material on your skin, the _Contact Resistance_ of your skin may have been as high as 5M Ohms (5,000,000 Ohms) - which would allow 900 µA (0.0009 Amp) to flow.
This is less than a lethal level, but will still do some harm.
If the _Contact Resistance_ of your skin was 100K Ohms, this would allow 45 mA (0.045 Amps) to flow.
This is a lethal level!
Since the maximum Short-Circuit Amperes of the Transformer is 30 mA (0.03 Amps), a shock with a _Contact Resistance_ of anything at 150K Ohms and below, will result in 30 mA flowing through the body, for a Ground-Fault type of shock (4.5 KV L-G)
doc thinks I blacked out for a brief time
This is most likely what saved your life!!!
OH OH, after the shock, my partner went to the base of the sign and tried to unhook the 120v feed for the sign, there was a arc between the neutral and ground as he unhooked the wires, why would it do that? I thought neutrals only carried 2v or so?
Well, this could have been from a number of things, but the most likely reason for the Arc is the Grounded Conductor (AKA "Neutral") is open between the Panelboard, where the Circuit(s) are derived, and some point outside of the Panelboard (like a junction box) - and there is some load on the Grounded Conductor.
Another likely reason may be from something connected mistakenly to the Grounded Equipment, instead of a Grounded Conductor for the Circuit feeding that Equipment.
A lot depends on the actual size of the Arc seen.
If the Arc was a small little "snap", this may be from normal Voltage Drop on the Branch Circuitry, and is a result of the Neutral Current dividing and flowing through both the Equipment Grounding Conductor ("Ground Wire", Conduit, etc.) and the Grounded Conductor.
If the Arc was large and loud, it may from an open Neutral scenario.
Good luck with you!
Hope this is helpful.