A and B feeds are easy to confuse

Examples are fictional local conventions. Unless another location is shown, the scope is DC01 / H1. Keep that scope with shortened identifiers.

When to use

Use this guide when the rack has several PDUs, the feed legend is unclear, or different teams call the same path by different names. The output is an identification record for each PDU and feed designation. A/B letters alone do not demonstrate electrical independence.

What to gather

Gather the rack schedule, approved power-path drawing and revision, PDU inventory, local identification legend, and accessible photographs. Record the drawing owner so disagreements reach someone who can resolve them.

Raritan describes using visibly different PDUs to distinguish feeds in a customer installation. That is a manufacturer example, not a universal color rule. Raritan source

Identification workflow

These steps are this library's recommended recordkeeping method.

1. Scope the rack. Record the full location and each PDU's existing identity. Keep a physical position such as rear-left separate from the feed designation.
2. Transcribe the evidence. Copy visible feed text exactly. Record missing or unreadable text explicitly; do not assign A or B from cable color or proximity.
3. Compare the documented paths. Match each PDU ID with its named upstream source in the approved drawing. Keep observed text and the approved designation in separate fields.
4. Prepare a consistent legend. Draft explicit feed text using the site's vocabulary. Have the power-record owner settle conflicting names before label production.
5. Close the identity changes together. After the approved labeling work, reconcile the PDU record, legend, and field evidence. Keep an unresolved path marked needs review.

The expanded procedures and fictional case below are original editorial recordkeeping guidance to adapt to the site's approved process.

Choose the starting branch

Start by identifying the kind of uncertainty. If the PDU identity and upstream relationship are supported but its feed wording is missing, prepare a missing-marking case. If a readable A or B disagrees with a controlled record, prepare a conflicting-designation case. If nobody can establish which inventory record represents the visible PDU, resolve that identity first. These branches have different evidence needs. Reprinting a clearer A will not resolve an uncertain PDU, and correcting an inventory duplicate will not establish its upstream path.

When several PDUs are present, create a bounded list before comparing names. Include the full rack address and the existing PDU identity for every included unit, even when only one sticker appears wrong. A three-PDU rack should produce three reviewed identity relationships, not two rows forced into an A/B template. Record any excluded unit and the reason it was outside the authorized observation scope. This makes the eventual completion claim specific enough for another reviewer to assess.

Treat physical position as finding assistance. A note such as rear-left, facing the rack from the rear service aisle, helps locate the observation. It does not decide the feed designation. If a local team uses left and right informally, preserve those words as aliases with a defined viewpoint and compare them with the approved vocabulary. Keep a proposed translation visibly proposed until the power-record owner agrees that it describes the intended object and documented path.

Build the evidence packet before drafting text

Start the packet with an object list, the power drawing identifier and revision, and the legend reference. Add one observation reference per PDU, with enough surrounding context to distinguish adjacent units. A cropped letter A can support a statement about the letter's condition, but it cannot by itself show which PDU carried it. Pair a context view with the detailed text or connect both observations through a controlled survey reference. Record the actual observation date separately from the drawing revision date.

Extract the upstream reference exactly as the drawing expresses it. If the record includes a distribution board and circuit, preserve both rather than replacing them with a broad source name. If the drawing only states a named power path, enter that reference and describe the missing detail. Do not extend a relationship by copying information from a similar rack. The reviewer needs to see the boundary between what the source establishes and what the survey still cannot establish.

The legend belongs in the packet because apparently different wording may be an approved equivalent or a real conflict. For example, the site might distinguish a short label face from a longer system designation. Record the rule that relates the two, including its revision. If no rule explains the relationship, leave the values separate. Avoid silently standardizing letters, punctuation, or descriptive words during transcription: the original wording is evidence of the condition you are trying to resolve.

Turn the comparison into specific decisions

Compare one PDU row at a time. First match the visible PDU identity to its inventory record. Then compare observed feed wording with the documented designation. Finally compare the linked upstream source with the cited drawing. Record the outcome of each comparison rather than one undifferentiated pass. An ID may match while its feed sticker is missing, or the sticker may match while the drawing reference is obsolete. Those outcomes call for different follow-up work and should remain distinguishable.

For a missing label, the proposed face can contain the PDU identity and approved textual feed designation once the owner has established them. For a conflicting label, preserve the old face in the case record and identify exactly which line changes. For an uncertain drawing, request the authoritative relationship from its owner and keep production text on hold. The worksheet should show who owns that resolution and what evidence is still needed, so an unresolved case can be resumed without repeating the survey.

Review the proposed label schedule across the whole included rack. Look for two rows that accidentally carry the same PDU identity, an upstream reference copied across unrelated rows, or a feed word that is unexplained by the legend. Inspect the full text intended for each face, including any optional location line. A final text review should use the actual label proof and intended viewing position; the schematic examples in this library do not establish physical size, mounting position, or material suitability.

Worked case: a copied template repeats the wrong feed

In this fictional case, DC01 / H1 / R301 contains PDU-G11-301 and PDU-G11-302. Both installed faces say FEED A. The survey record FEED-G11-301 captures each PDU identity, its visible words, and separate observation references. Drawing PWR-G11-301 revision 4 associates PDU-G11-301 with the site's Feed A designation and PDU-G11-302 with Feed B. The reviewer has not yet established whether the field text or the drawing is stale, so the initial result is a conflict on the second row.

The records owner compares the inventory and the approved change history. In the fictional resolution, those records support the drawing relationship and identify a label schedule copied from the first PDU. The owner documents that decision as DEC-G11-301. The replacement face is PDU-G11-302 followed by FEED B; the PDU identity remains unchanged. The first unit's face is retained. This is an identification correction supported by a recorded decision, not an inference that differently named feeds have any particular engineering characteristic.

Closeout checks the replacement against the approved text and records a new observation reference, EV-G11-303. The schedule now assigns one reviewed face to each PDU, the inventory links to the same drawing revision, and the legend explains the A/B terms used. The old face remains visible in the case history, and the obsolete loose label is accounted for under the change. The completed case states which identity discrepancy was corrected; it does not broaden the conclusion into a claim about capacity, redundancy, or an operating procedure.

Variations that need an explicit record choice

A replaced PDU may occupy the former unit's physical position while carrying a different asset identity. In that situation, retain the location relationship and review the new object's feed association through the replacement record. Do not reuse the former PDU record simply because its sticker position is convenient. Conversely, a renamed drawing reference may describe the same physical object. Keep the old name as historical context and document the approved crosswalk rather than manufacturing a second PDU to accommodate a new alias.

If a facility uses designations other than A and B, keep its actual vocabulary. The worksheet can record additional paths without changing the method: each physical PDU still needs its own identity, designation, upstream reference, legend, and review state. If the power path is described differently across systems, assign an owner to the translation. A note that two phrases are locally equivalent should identify the authority and the exact scope of that equivalence, instead of becoming an unexplained universal substitution.

During a phased relabeling effort, distinguish a reviewed record from an installed correction. A batch may be ready for printing while the field still carries older text. Keep those stages visible and identify the racks included in each wave. If a later drawing revision affects one wave, review its affected rows rather than overwriting the entire register's history. A practical completion statement names the included PDUs and remaining exceptions so the next shift can determine which faces are current.

Evidence needed to close the discrepancy

Use the final check to answer a narrow question: does this identified PDU now carry the reviewed designation, and do its linked records agree? The evidence should connect the final face to the PDU, the accepted decision, and the supporting drawing revision. A label printer screenshot proves what was prepared; it does not prove what was installed. A photograph of an installed face proves observable text; its relationship to the approved path still depends on the referenced record and responsible review.

If any of those links remain uncertain, keep the case open with a specific missing item. Examples include an unreadable PDU identity, an unapproved legend translation, or a drawing revision awaiting confirmation. Assign the next action to a role that can resolve that item. This editorial workflow intentionally treats unresolved information as a useful result when it is accurately bounded, owned, and retrievable, rather than hiding it behind a completed checkbox.

Join the documented power chain through the whip

An upstream reference becomes harder to review when a record skips an intermediate identified object. For a documented chain that includes a whip, retain its identity and both recorded endpoints between the panel/circuit and PDU. Continue through the individual outlet, cord, and device inlet. Give each relationship its own source reference; a single drawing number at the bottom of a worksheet can hide which links the drawing actually supports.

The following specimen is fictional DC01/H1, rack R024. Every relationship is transcribed from example records; none is a live electrical verification. E-G11-501 revision 3 identifies the upstream path as FEED A. REG-G11-501 revision 2 records the two cord destinations. The short outlet names O07 and O08 are scoped to PDU-G11-501.

Joining those rows gives both device inlets the same documented FEED A path. Accepted design reference DES-G11-501 revision 4 calls for separately designated A and B paths at this example device. Record the discrepancy as “both inlet records resolve to PDU-G11-501 / FEED A; conflicts with cited design.” That finding is more useful than “B label missing,” which prematurely assumes a printing problem. It also avoids treating two different cord colors as evidence that the records must be wrong.

Send the joined evidence to the electrical records owner. A missing whip-to-PDU reference should remain a missing relationship; do not bridge it from physical proximity. If the owner finds that the as-built or cord register is stale, link the accepted replacement reference and retain the superseded relationship in history. Closure requires a reviewed disposition for each inlet and every disputed link, plus the corresponding identification-record updates.

This is an identity comparison. A matching chain does not establish supply independence, electrical condition, or an operating decision. Keep those conclusions with the appropriate engineering and work-practice evidence. OSHA electrical work practices

Worked example

Example only: fictional identities and relationships.

SCOPE: DC01 / H1 / R014
H1 / R014        DOCUMENTED SOURCE     FEED TEXT
PDU-A01          UPS-01 / RPP-03       FEED A
PDU-B01          UPS-02 / RPP-04       FEED B

These rows explain which record belongs to which PDU. They do not establish redundancy, capacity, or permission to disconnect.

Common mistakes

• Treating rear-left as a permanent synonym for Feed A.
• Using color without readable feed text.
• Copying a neighboring rack's upstream source.
• Closing the issue while the drawing and label still disagree.

Verification

• Each PDU resolves to one inventory record.
• Observed and documented feed names are compared.
• The upstream reference includes the drawing revision.
• The local legend explains every designation used.
• Unresolved relationships have an owner.

Worksheet: A/B feed identification worksheet

Filled example row - fictional; no live verification.

FAQs

Should A always be one particular color?

Use the site's approved legend and readable text. This guide does not prescribe feed colors.

Can a matching record prove two feeds are independent?

No. Independence needs the appropriate engineering evidence; this worksheet records identity only.

Can a PDU position be printed on the same face as its feed name?

It can be proposed as a separate location aid under the site's labeling process. State the viewpoint and keep the position distinct from the feed field. Review what happens when equipment moves; a position line that is no longer current should not remain as unexplained identification text.

What if the sticker says A but the legend says FEED A?

Record both exact values and consult the local legend. If the approved rule makes them equivalent, cite that rule and record the comparison result. If the rule does not address the difference, ask the records owner to resolve the wording rather than silently treating them as the same.

Can I finish the readable PDUs while one remains uncertain?

Yes, if the completion record names the reviewed population and the open exception explicitly. Close the supported rows individually and retain the uncertain unit's identity, evidence gap, owner, and next action. Do not mark the entire rack reviewed in a way that includes the unconfirmed relationship.

Does an old photo remain useful after replacement?

It remains useful as historical observation evidence when its object identity and date are clear. Link it to the former state and retain a new observation for the replacement. An old image should not serve as current confirmation merely because the replacement occupies the same rack position.

More worked label examples

Two additional ways to apply this guide. Keep the exact identifiers and relationships consistent with your own approved records.

SCOPE: DC01 / H1 / R101; legend LEG-G11-101 r2
PDU LABEL FACES
+---------------------------+  +---------------------------+
| PDU-G11-101               |  | PDU-G11-102               |
| FEED A                    |  | FEED B                    |
| REF PWR-G11-101 r4        |  | REF PWR-G11-101 r4        |
+---------------------------+  +---------------------------+

DOCUMENTED MAPPING
PDU-G11-101 -> FEED A -> DB-G11-101 / CIRCUIT 12
PDU-G11-102 -> FEED B -> DB-G11-102 / CIRCUIT 18
Observed text: A and B; record comparison: matched
Owner review: EV-G11-101; legend records local designations
Label match is identification evidence, not a safety test

SCOPE: DC01 / H1 / R201; finding FEED-G11-201
OBSERVED LABEL FACE
+--------------------+
| PDU-G11-201        |
| FEED A             |
+--------------------+

OBSERVATION: PDU-G11-201 says FEED A
RECORD: PWR-G11-201 r5 says FEED B, DB-G11-202 / C06
INITIAL STATUS: unresolved; do not infer from sticker color

ILLUSTRATIVE OWNER DISPOSITION: record verified, text wrong
REPLACEMENT FACE: [PDU-G11-201 | FEED B]
Decision EV-G11-201 -> replacement under CH-G11-201
Final check EV-G11-202 -> face matches approved record

Sources and applicability

• Raritan: Advanced engineering ↗

  Manufacturer A/B differentiation example; no universal color code or proof of feed independence.

  Read scope and linked guides
• OSHA: 29 CFR 1910.333 ↗

  Electrical work-practice boundary only. The joined chain and fictional design discrepancy are original recordkeeping examples, with no operation or independence test.

  Read scope and linked guides

Planning guides and companion documents

• Create a cable-color legend people can use
• Remote-hands cabinet identification brief
• Cable-color meaning and transition planning register

Related guides