SCP Foundation

SCP-XXXX is to be contained in a 1 ft x 1ft x 1ft cubic locker within site-28, lined with rubber in order to prevent it from extracting electricity from objects.

First off, don't use feet. The Foundation is an international organization and uses the system that the international community uses: the metric system. Furthermore, even though your SCP does have a specific radius effect, this is still too specific. You can simply state that the locker has to be at least larger than the radius. Heck, since you state rubber effectively neutralizes it, you can just leave it in a box insulated against electricity.

You don't have to state "in order to," really anywhere in the special containment procedures. After all, it's automatically assumed that the special containment procedures are there to counter an SCP's specific abilities. I would recommend trimming down your procedures to:

SCP-XXXX is a glass jar, with a regular mouth (60 mm) and a height of 3.8 inches.

Two things. Don't use the number(x) formatting because it's too specific and not really applicable here. It's only really applicable in situations involving pharmaceutical dosages. Also, use the metric system, not inches(centimeters).

It holds no anomalous features in its form.

A jar with a mouth is a rather anomalous feature if you ask me.

The manufacturer of the jar is unknown, as the object holds no serial numbers or identifying features of any kind.

I don't really think this is necessary. The reason being that I'm not exactly sure if jars even get serial numbers. Then again, I'm not a jar expert. In my opinion I think you should get rid of this, or move it up so it appears with the physical description, and skip to the electricity activity. Simply so there don't appear to be any speed bumps in reading.

When the jars lid is removed

Should be "jar's."

the object begins to absorb surrounding electricity from any electrical device around it within a 0.2286 meter radius

The tense is a bit wonky. So the sentence starts with "when the…" so this part should be written as "the object will begin…"

0.2286 meters is a bit of an eyesore and it's far more likely that the Foundation would turn it into 22.9, or 23, centimeters.

Beyond this, I still think this sentence can be tightened up into "the object will begin to absorb any electricity within a 23 cm radius." The same information is conveyed(you can assume that no electricity is going to be pulled from the box it's in for example), and it's more concise.

(Note: The absorption is impossible through materials incapable of conducting electricity).

Personally, I think this is important enough to be free of parentheses. You can easily integrate this into the main text by quickly mentioning that electricity being absorbed does not display any anomalous properties and can still be stopped with insulating materials.

The jar can only withhold approximately 2.7 amps of electricity, absorbing the energy at the pace of a device with 144 ohms.

This is a little bit…much. I can't really picture what 2.7 amps of electricity looks like. What I can picture is 5 light bulbs so I'd recommend just keeping it at that. If you really want to keep these numbers, I believe it should be fine to slot them into some parentheses.

As this occurs, the inside of the jar will begin to emit a bright yellow light.

This can be trimmed down and added directly to the light-bulb sentence:

"these measurements align with that of five light bulbs, and the jar will begin to shine correspondingly"

If the lid is removed while the jar still holds light (electricity), SCP-XXXX will emit an electromagnetic pulse at the exact same radius as its absorption length of 0.2286 meters. This pulse has the potential to disrupt surrounding electronics, and thus causes a threat to areas of importance such as hospitals, military locations, or even the sites of the Foundation; However, the pulse does not have long lasting effects.

I think this part suffers because of the radius. As a reader, it's a little hard to believe that 23 centimeters(which isn't even a foot) is large enough to be considered a threat to entire military installations. To do so, this thing would have to go off at exactly the right location. And even then, auxiliary/emergency systems would undo the effects.